cmake: Update minimum version to allow building with CMake 4+

[abaire]

pyfatx can't be installed on Windows with the latest CMake release due to removal of support for CMake 3.5 and below features.

     -- Building for: NMake Makefiles
      CMake Error at CMakeLists.txt:18 (cmake_minimum_required):
        Compatibility with CMake < 3.5 has been removed from CMake.

        Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
        to tell CMake that the project requires at least <min> but has been updated
        to work with policies introduced by <max> or earlier.

        Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.