Fix cmake error for 4.x

[HIllya51]

On cmake-4.1.0, when openlibm is included as a subdirectory, it causes an error:
Setting CMAKE_PROJECT_VERSION can also fix this issue, but I don't really prefer doing so.

CMake Error at openlibm/CMakeLists.txt:569 (string):
  string sub-command REPLACE requires at least four arguments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.09%. Comparing base (c984c27) to head (7cfd051).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #333   +/-   ##
=======================================
  Coverage   72.09%   72.09%           
=======================================
  Files         233      233           
  Lines        6139     6139           
  Branches     1607     1607           
=======================================
  Hits         4426     4426           
  Misses       1420     1420           
  Partials      293      293           

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