chore: fix logic in file-diff github action

[castastrophe]

Description

File diff GitHub Action has a small logic error when determining if a package has been removed or added. This PR fixes that logic error.

• Updates logic to the existing isRemoved and isNew functions which are being used elsewhere for the same determination

How and where has this been tested?

Please tag yourself on the tests you've marked complete to confirm the tests have been run by someone other than the author.

Validation steps

• The S2 foundations branch is using this update and the Diff table is correct now

To-do list

• I have read the contribution guidelines.
• ✨ This pull request is ready to merge. ✨

[changeset-bot]

⚠️ No Changeset found

Latest commit: 778842a

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

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[github-actions]

🚀 Deployed on https://pr-3161--spectrum-css.netlify.app

[github-actions]

File metrics

Summary

Total size: 4.31 MB^*

🎉 No changes detected in any packages

* Size determined by adding together the size of the main file for all packages in the library.
* Results are not gzipped or minified.
* An ASCII character in UTF-8 is 8 bits or 1 byte.