ci: add code scanning

[barmac]

Proposed Changes

Standard stuff. GH scans code and warns us.

Checklist

Ensure you provide everything we need to review your contribution:

• Your contribution meets the definition of done
• Any new additions or modifications are consistent with the existing UI and UX patterns
• Pull request description establishes context:
  • Link to related issue(s), i.e. Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}
  • Brief textual description of the changes
  • Screenshots or short videos showing UI/UX changes
  • Steps to try out, i.e. using the @bpmn-io/sr tool

[philippfromme]

Let's see what happens. 👍🏻

[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.