[FIX,INFRA] cmake: version variables cannot be forced

[eseiler]

Forced cache will cause the variable to be always set to the value defined in the package lock.
We actually want to be able to overwrite this.

Preferably, we would like to

• Overwrite if given on CLI. Otherwise, use default.
• On reconfigure, revert to default if not given.
• Have the variables available in the parent project (CPM version update script).

This doesn't really seem possible, see https://github.com/eseiler/misc/tree/main/cmake_set for some examples.

The drawback of CACHE is that changed default versions are not honored on a simple reconfigure.

[seqan-actions]

Documentation preview available at https://docs.seqan.de/preview/seqan/seqan3/3361

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.11%. Comparing base (5d07997) to head (4140e50).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3361   +/-   ##
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  Coverage   98.11%   98.11%           
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  Files         270      270           
  Lines       11913    11913           
  Branches      103      103           
=======================================
  Hits        11689    11689           
  Misses        224      224           

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