Fix install of /etc/profile.d/mamba.sh when `--prefix` is set

[flying-sheep]

Fixes #4055

TODO: Is updating cmake_minimum_required correct or is there a way for people to get that policy active with lower versions?

[henryiii]

You can do a range, then the highest one in the range is used for policy defaults.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 63.58%. Comparing base (6f11ca2) to head (2456218).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4057   +/-   ##
=======================================
  Coverage   63.57%   63.58%           
=======================================
  Files         315      315           
  Lines       38562    38562           
  Branches     2950     2950           
=======================================
+ Hits        24517    24518    +1     
+ Misses      13976    13975    -1     
  Partials       69       69           

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[flying-sheep]

@henryiii is this good to go?