Update 11ty-publish workflow to use git-auto-commit-action

[kfranqueiro]

This update resolves spurious errors in the publish workflow in cases where a merge to main results in no changes to push to gh-pages.

• Example of the type of error this addresses
• Example of the same type of run succeeding with this change
• Example of a run completing with this change, operating as usual when there are changes to commit to gh-pages
  • Commit from this example

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