Tell dependabot to ignore gomega

[dmikusa]

Summary

Gomega releases often, and it creates a lot of churn. It is also a dev dependency, so we can just update it weekly when we update dependencies.

Use Cases

Less churn.

Checklist

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