CMake: Bump minimum version

[jschueller]

Avoid the annoying deprecation warning:

$ cmake ..

CMake Deprecation Warning at CMakeLists.txt:4 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

-- The C compiler identification is GNU 14.1.1
...