Pin CMake to lower than 4 in CI

[JeanChristopheMorinPerso]

Fixes #2015

Rez needs features from CMake 2, but CMake 4 dropped support for these.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.01%. Comparing base (8fde5c2) to head (0ed2bd5).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2021      +/-   ##
==========================================
+ Coverage   59.77%   60.01%   +0.24%     
==========================================
  Files         163      163              
  Lines       20005    20098      +93     
  Branches     3494     3494              
==========================================
+ Hits        11958    12062     +104     
+ Misses       7231     7224       -7     
+ Partials      816      812       -4     

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