chore: expire delegations if later pushes touch sensitive files

[bryangingechen]

This PR adds a restrict_to_paths setting per leanprover-community/bors-ng#50 so that delegated PRs will have their delegations expire immediately if the author pushes changes to any files outside the following locations:

• "Archive/**",
• "Counterexamples/**",
• "docs/**",
• "DownstreamTest/**",
• "Mathlib/**",
• "MathlibTest/**",
• "widget/**",
• "Archive.lean",
• "Counterexamples.lean",
• "docs.lean",
• "Mathlib.lean",

As a consequence, changes outside these directories after delegation must be re-approved by a maintainer.

(bors will do its best to distinguish from changes to the code coming from the master branch so except in cases of PRs that touch a large number of files, merging master should be safe, even if there are changes outside the above directories.)

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[github-actions]

PR summary 3f1f3d0f24

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

---

No changes to strong technical debt.

No changes to weak technical debt.

Current commit 3f1f3d0f24
Reference commit cca4f7de20

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

[grunweg]

Thanks! I'd like to have another pair of eyes on the glob patterns, but the policy seems good to me.
maintainer merge

[github-actions]

🚀 Pull request has been placed on the maintainer queue by grunweg.

[SnirBroshi]

This is interesting, can you please elaborate on the goal with it? Is it to protect the CI servers or other contributors who have cloned the project?