Updating KDE Frameworks minimum cmake requirements to 3.23

[Albert Astals Cid]

I would like to increase cmake requirement of KDE Frameworks to 3.23.

This way we can use CMAKE_VERIFY_INTERFACE_HEADER_SETS that checks that each 
of the headers is "compilable" on its own.

Proof of concept on 
https://invent.kde.org/frameworks/karchive/-/merge_requests/80

Where i have changed the code so that it compiles but so that kar.h would not 
be "compilable" on it's own.

I'm mostly sure that our headers are possibly good, but some extra checking 
does not hurt.

cmake 3.23 was released on July 2022.

Looking at https://repology.org/project/cmake/badges it seems it should not be 
problematic at all.

What do you all think?

Cheers,
  Albert

P.S: I guess it'd be better to come up with a policy but I had no idea what to 
suggest :D