Vet actions with zizmor

[philipqueen]

While looking into the recent Ultralytics vulnerability, I came across zizmor. This is a security linting tool for github actions. I decided to run it as part of our recent push to ensure our actions security is solid.

Changes:

• remove the unused ci.yml - this only triggered when a multi year old branch was edited, might as well reduce the attack surface and clean out some old code.
• add persist-credentials: false to all checkout actions. this reduces the chance of accidentally leaking tokens: https://woodruffw.github.io/zizmor/audits/#artipacked
• Change to Trusted Publishing - this is an "info" level warning, but probably still a good idea. There's more info here: https://woodruffw.github.io/zizmor/audits/#use-trusted-publishing
• add a workflow to run zizmor whenever a workflow is changed - meta CI/CD, if you will - to ensure we don't regress in the future

[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.