Update gha-dart-oss and add no_entrypoint_imports check

[sydneyjodon-wk]

Motivation

Changes

Release Notes

Review

See CONTRIBUTING.md for more details on review types (+1 / QA +1 / +10) and code review process.

QA Checklist

• Tests were updated and provide good coverage of the changeset and other affected code
• Manual testing was performed if needed
  • Steps from PR author:
  • Anything falling under manual testing criteria outlined in CONTRIBUTING.md

Merge Checklist

While we perform many automated checks before auto-merging, some manual checks are needed:

• A Frontend Frameworks Design member has reviewed these changes
• There are no unaddressed comments - this check can be automated if reviewers use the "Request Changes" feature
• For release PRs - Version metadata in Rosie comment is correct