Fix pre-push hook to fail if working tree dirty

[mcmire]

Explanation

Now that we've instructed the lint pipeline to update the ESLint warning thresholds file, if you introduce changes to lint violations prior to pushing, and you have the pre-push Git hook installed, you could forget to push changes to this file.

This commit extracts the "working tree dirty" check that we perform in the lint-build-test GitHub workflow to a script so that we can not only call it in the workflow but also after running yarn lint in the pre-push hook.

Note that you'll need to re-run yarn simple-git-hooks for this change to take effect.

References

Changelog

(N/A, developer-only change)

Checklist

• [x] I've updated the test suite for new or updated code as appropriate
• [x] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• [x] I've highlighted breaking changes using the "BREAKING" category above as appropriate
• [x] I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

[github-advanced-security[bot]]

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[mcmire]

^ I think that comment may be a misfire.