Rewrite pubspec with a comment-preserving YAML library in patch_pubspec_version.py

[jtullos-bt]

Description

Fixes #6655.

The CI step that publishes flet-build-template.zip rewrites the pubspec's flet dependency via .github/scripts/patch_pubspec_version.py, which round-trips the file through yaml.safe_load + yaml.dump and discards all comments, including the cookiecutter conditional markers that gate the app/app.zip assets to web builds. The published zip therefore declares the assets unconditionally, and desktop builds require a file the packaging step never produces.

This PR rewrites the pubspec in patch_pubspec_version.py with a comment-preserving YAML library (ruamel.yaml round-trip mode). Tested against the v0.86.0.dev1 template in both patch modes; the conditionals survive and the dependency rewrite is unchanged.

Test code

Repro repo demonstrating the failure on a stock GitHub macOS runner: https://github.com/jtullos-bt/flet-build-appzip-repro (failing run: https://github.com/jtullos-bt/flet-build-appzip-repro/actions/runs/28890234132)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Additional details

The same patch step runs on stable release tags (with an exact version pin instead of a git ref), so an eventual 0.86.0 stable template zip is expected to carry the same defect unless the script is fixed first.

Summary by Sourcery

Preserve YAML comments when patching the pubspec dependency in the build template patching script so template conditionals continue to work.

Bug Fixes:

• Fix loss of YAML comments and template conditionals when rewriting pubspec during the build template publish step.

Enhancements:

• Switch the pubspec patching script to use ruamel.yaml round-trip mode to retain comments and original formatting while updating the flet dependency.

Build:

• Update the script dependency metadata to require ruamel.yaml instead of PyYAML for the pubspec patching step.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[sourcery-ai]

We've reviewed this pull request using the Sourcery rules engine

[FeodorFitsner]

The fix is not relying anymore on jinja expressions in yaml comments (that was fragile): https://github.com/flet-dev/flet/pull/6654/changes#diff-ec4a6066761029ec8d50029894940e3c1fd754829c0caad08292127fdbd1a09f

But I don't mind using ruamel for preserving comments during CI patching.

Can you please:

• re-target your PR to flet-0.86 branch.
• add a record to changelog.

Thanks!

[jtullos-bt]

I had to close this, I'm not sure I can give you a good answer to the "Your Employer" section of the CLA. It might have been fine, but I would rather not sign a legal representation I havne't verified.

[FeodorFitsner]

That's fine, thanks!

[jtullos-bt]

The fix is not relying anymore on jinja expressions in yaml comments (that was fragile): https://github.com/flet-dev/flet/pull/6654/changes#diff-ec4a6066761029ec8d50029894940e3c1fd754829c0caad08292127fdbd1a09f

But I don't mind using ruamel for preserving comments during CI patching.

Can you please:

• re-target your PR to flet-0.86 branch.
• add a record to changelog.

Thanks!

sorry, see my comment below :(