Add zizmor for GHA security analysis

[tim-schilling]

Code sourced from: https://docs.zizmor.sh/integrations/#github-actions

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.

[github-advanced-security]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[matthiask]

Thanks. I think it's a good idea to try this out.

[tim-schilling]

We were discussing this in django-commons/best-practices#13 and decided on limiting it to only run based on .github/ files. What do you think about that?