build: temporarily stop publishing to GCR

[mhdawson]

Refs: https://github.com/orgs/paketo-buildpacks/discussions/253

Summary

Temporarily disable publishing to GCR as the paketo-community version seems to have disappeared 3 weeks ago.

Use Cases

Checklist

• [x] I have viewed, signed, and submitted the Contributor License Agreement.
• [x] I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• [x] I have added an integration test, if necessary.
• [x] I have reviewed the styleguide for guidance on my code quality.
• [x] I'm happy with the commit history on this PR (I have rebased/squashed as needed).