Fix Rubocop Scanning

[alexfinnarn]

I tried adding a Rubocop GitHub integration where you click a button and GitHub starts a commit with a default configuration file. Most of the time, these things work out of the box; however, this time I get an error about uploading the SARIF file.

Could be about the matrix part I deleted in the top-level job: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstrategy

But the error is about invalid SARIF file syntax: https://docs.github.com/en/code-security/secure-coding/sarif-support-for-code-scanning

Acceptance Criteria

• Add Rubocop to the Gemfile so it isn't added via the GH Action
• Run Rubocop locally to see things pass and a proper SARIF file is generated
• Modify rubocop-analysis.yml so that it works on GH CI runs