CMake warning when using FetchContent

[nilsvu]

I'm getting this warning when using FetchContent_Declare as listed in the README:

 CMake Deprecation Warning at _deps/yaml-cpp-src/CMakeLists.txt:2 (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.

Can this be fixed?

[pbosetti]

I second this one. Now that versions < 3.5 are officially deprecated, unless there is a specific reason this is just an unnecessary warning that could distract from serious ones. Shall we make a PR?

[K20shores]

Bumping, this has now caused one of our CI issues to fail since cmake has officially dropped support for cmake < 3.5

[K20shores]

Looks like there's a PR that could fix this with #1351