chore(ci): Update SDK Size analysis workflow to trigger on label updates

[github-actions]

Note

The pull request "chore(ci): Update SDK Size analysis workflow to trigger on label updates" was created by @itaybre but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

I forgot to add the labeled trigger for PRs for this workflow which caused this workflow only to trigger when opening a PR, but not when adding the label.

This should fix this.

#skip-changelog

[linear]

COCOA-977