Add changeset formatting check

[hsubox76]

Add a yarn changeset status check to the changeset checker, which catches changeset formatting errors. It will still show the "missing packages" warning, and will also show any "yarn changeset status" errors if found, or both, if both are found.

The check will fail if "yarn changeset status" errors are found (blocking merge), but won't fail on "missing packages", it will only print the warning in the comment.

[changeset-bot]

⚠️ No Changeset found

Latest commit: deb31fa

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]

Changeset File Check ✅

• No modified packages are missing from the changeset file.
• No changeset formatting errors detected.

[google-oss-bot]

Binary Size Report

Affected SDKs

No changes between base commit (f4110cc) and head commit (b565799).

Test Logs

• Base (f4110cc5): https://github.com/firebase/firebase-js-sdk/actions/runs/322640975
• Head (b5657993): https://github.com/firebase/firebase-js-sdk/actions/runs/324451560