Add codeQL scanning

[jlaehne]

Description of the change

Add github action for code scanning using the codeQL engine.

Run on PR, push and weekly schedule.

Progress of the PR

• Change implemented (can be split into several points),
• [n/a] update user guide (if appropriate) - no separate dev guide yet,
• add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting changelog entry in the readthedocs doc build of this PR (link in github checks)
• ready for review.

[codecov]

Codecov Report

Merging #26 (8fa51e1) into main (72eea4e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #26   +/-   ##
=======================================
  Coverage   82.82%   82.82%           
=======================================
  Files          40       40           
  Lines        8051     8051           
  Branches     1859     1859           
=======================================
  Hits         6668     6668           
  Misses        921      921           
  Partials      462      462           

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