ci: update check for changeset workflow with local bash script

[Copilot]

Closes #

Recreates the changed-files changeset guard as a local GitHub Action and updates the changeset workflow to use it instead of brettcannon/check-for-changed-files@v1. The workflow now grants explicit read-only permissions and passes github.token to the local action for listing PR files.

The upstream workflow hasn't been updated for a little bit so this helps us prevent using outdated actions (was seeing the Node.js warning which is what prompted this)

Changelog

New

• Added a local .github/actions/check-for-changed-files GitHub Action.

Changed

• Updated .github/workflows/check_for_changeset.yml to use the local action instead of the external action.

Removed

• Removed the workflow dependency on brettcannon/check-for-changed-files@v1.

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; CI/infrastructure-only change, so no package release or changeset is needed.

Testing & Reviewing

• Baseline before edits: npm install, npm run build, npm test -- --run, npm run type-check, npm run lint, npm run lint:css, npm run format:diff
• Final validation: node --check .github/actions/check-for-changed-files/index.js, npx eslint .github/actions/check-for-changed-files/index.js --max-warnings=0 --cache, npm run build, npm test -- --run, npm run type-check, npm run lint, npm run lint:css, npm run format:diff
• Smoke-tested non-PR and skip-label action paths locally.
• Secret scanning passed for changed files.
• Code review/CodeQL validation: initial CodeQL scan passed with 0 alerts; a later validation run timed out after review comments were returned, and the tool instructed not to rerun it. Review comments were addressed with targeted validation afterward.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github-ui (Learn more about how to run integration tests)

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7e0dde9

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[joshblack]

@copilot instead of having a script for this could it just be a bash script in the workflow?

[Copilot]

@copilot instead of having a script for this could it just be a bash script in the workflow?

Updated the PR to use an inline bash step in .github/workflows/check_for_changeset.yml and removed the local JavaScript action files. Addressed in 731fe14.

[joshblack]

The failure-message should be a comment on the Pull Request (and make sure to re-use one if it already exists instead of always making a new one)

[joshblack]

@copilot The failure-message should be a comment on the Pull Request (and make sure to re-use one if it already exists instead of always making a new one)

[Copilot]

@copilot The failure-message should be a comment on the Pull Request (and make sure to re-use one if it already exists instead of always making a new one)

Addressed in c58b337 by having the workflow create or update a marked PR comment for the missing-changeset failure message.