gh-143706: Fix sys.argv not set during multiprocessing forkserver __main__ preload

[gpshead]

The forkserver was not passing sys.argv to its main() function, causing sys.argv to be empty during __main__ module import in child processes. This fixes a non-obvious regression inadvertently introduced by the gh-126631 main preloading fix.

@duaneg FYI

• Issue: sys.argv no longer correct during main module execution using forkserver #143706

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @gpshead for commit 30b347f 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F143717%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[duaneg]

LGTM

[miss-islington-app]

Thanks @gpshead for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @gpshead, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 298d5440eb83f2dfd5651bac86d1592ec358d54c 3.13

[bedevere-app]

GH-143763 is a backport of this pull request to the 3.14 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x (tier-2) has failed when building commit 298d544.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/725/builds/12531) and take a look at the build logs.
4. Check if the failure is related to this commit (298d544) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/725/builds/12531

Failed tests:

• test_urllib2net

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 23, done.        
remote: Counting objects:   4% (1/23)        
remote: Counting objects:   8% (2/23)        
remote: Counting objects:  13% (3/23)        
remote: Counting objects:  17% (4/23)        
remote: Counting objects:  21% (5/23)        
remote: Counting objects:  26% (6/23)        
remote: Counting objects:  30% (7/23)        
remote: Counting objects:  34% (8/23)        
remote: Counting objects:  39% (9/23)        
remote: Counting objects:  43% (10/23)        
remote: Counting objects:  47% (11/23)        
remote: Counting objects:  52% (12/23)        
remote: Counting objects:  56% (13/23)        
remote: Counting objects:  60% (14/23)        
remote: Counting objects:  65% (15/23)        
remote: Counting objects:  69% (16/23)        
remote: Counting objects:  73% (17/23)        
remote: Counting objects:  78% (18/23)        
remote: Counting objects:  82% (19/23)        
remote: Counting objects:  86% (20/23)        
remote: Counting objects:  91% (21/23)        
remote: Counting objects:  95% (22/23)        
remote: Counting objects: 100% (23/23)        
remote: Counting objects: 100% (23/23), done.        
remote: Compressing objects:   7% (1/13)        
remote: Compressing objects:  15% (2/13)        
remote: Compressing objects:  23% (3/13)        
remote: Compressing objects:  30% (4/13)        
remote: Compressing objects:  38% (5/13)        
remote: Compressing objects:  46% (6/13)        
remote: Compressing objects:  53% (7/13)        
remote: Compressing objects:  61% (8/13)        
remote: Compressing objects:  69% (9/13)        
remote: Compressing objects:  76% (10/13)        
remote: Compressing objects:  84% (11/13)        
remote: Compressing objects:  92% (12/13)        
remote: Compressing objects: 100% (13/13)        
remote: Compressing objects: 100% (13/13), done.        
remote: Total 13 (delta 10), reused 2 (delta 0), pack-reused 0 (from 0)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
Note: switching to '298d5440eb83f2dfd5651bac86d1592ec358d54c'.

You are in 'detached HEAD' state. You can look around, make experimental
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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 298d5440eb8 gh-143706: Fix sys.argv not set during multiprocessing forkserver `__main__` preload (#143717)
Switched to and reset branch 'main'

make: *** [buildbottest] Error 2

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x (tier-2) has failed when building commit 298d544.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/725/builds/12532) and take a look at the build logs.
4. Check if the failure is related to this commit (298d544) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/725/builds/12532

Failed tests:

• test_urllib2net

Summary of the results of the build (if available):

==

Click to see traceback logs

Note: switching to '298d5440eb83f2dfd5651bac86d1592ec358d54c'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 298d5440eb8 gh-143706: Fix sys.argv not set during multiprocessing forkserver `__main__` preload (#143717)
Switched to and reset branch 'main'

make: *** [buildbottest] Error 2