fix the warning CPM: Your project is using an unstable development version of CPM.cmake. when using FetchContent

[flagarde]

This PR fix the warning

CMake Warning at build/_deps/cpm-src/cmake/CPM.cmake:80 (message):
  CPM: Your project is using an unstable development version of CPM.cmake.
  Please update to a recent release if possible.  See
  https://github.com/cpm-cmake/CPM.cmake for details.
Call Stack (most recent call first):
  build/_deps/cpm-src/CMakeLists.txt:37 (include)

when using FetchContent to download CPM.

describe --tags --long command :
Always output the long format (the tag, the number of commits and the abbreviated commit name) even when it matches a tag. This is useful when you want to see parts of the commit object name in "describe" output, even when the commit in question happens to be a tagged version. Instead of just emitting the tag name, it will describe such a commit as v1.2-0-gdeadbee (0th commit since tag v1.2 that points at object deadbee…​.).

so if the HEAD is exactly at some tags matching v*..-0-* then Head is on a release and so not a development.