Run CD also on push to main

[N-Wouda]

This PR:

• fixes a CD build issue on Windows by bumping to CIBW 2.16.5
• provides a workaround for macOS's inability to handle std::optional::value
• fixes uploading and downloading artefacts of the same name

Since this stuff's horribly annoying, from now on we're also going to test run the CD every time we push to main.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 94.98%. Comparing base (75e4fd4) to head (91588a9).
Report is 1 commits behind head on main.

❗ Current head 91588a9 differs from pull request most recent head cd17ded. Consider uploading reports for the commit cd17ded to get more accurate results

Files	Patch %	Lines
pyvrp/cpp/ProblemData.cpp	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #544   +/-   ##
=======================================
  Coverage   94.98%   94.98%           
=======================================
  Files          73       73           
  Lines        3012     3012           
  Branches      247      247           
=======================================
  Hits         2861     2861           
  Misses         66       66           
  Partials       85       85           

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