CI: adding workflow_dispatch

[bsipocz]

I see a lot of failures of tests for the dependabot PRs, would be useful to be able to trigger runs for easier cross check whether something is already present on main.

[stefanv]

The manual trigger should probably not be active on the wheel builder, though? Or should it?

[bsipocz]

My thought process was that it enables a manual rebuild, but indeed, it may not be actually useable.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.19%. Comparing base (e153def) to head (d0375c9).
⚠️ Report is 40 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #84   +/-   ##
=======================================
  Coverage   95.19%   95.19%           
=======================================
  Files           1        1           
  Lines         104      104           
=======================================
  Hits           99       99           
  Misses          5        5           

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