cmake: bump min version

[dakejahl]

bump min version to 3.16.3, which is what Ubuntu 20.04 ships with

Fixes this deprecation warning

CMake Deprecation Warning at CMakeLists.txt:102 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  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.

[dakejahl]

Looks like CI still uses older cmake for some targets. Reducing to 3.10 to just get rid of the warning.