kdev-python: Use CMake FindPython3

[Casian Andrei]

Use FindPython3 instead of FindPythonInterp and FindPythonLibs

Fixes CMake warning regarding CMP0148 - deprecation of FindPythonInterp 
and FindPythonLibs.

Initially tested using a python3.12, but kdevelop crashes and there are 
kdev-python errors in the logs, so kept max version to 3.11.

Tested with a local compiled python3.9. When the python3.9 was compiled 
without --enable-shared, CMake didn't work, as expected. When compiled 
with --enable-shared, CMake worked fine. Built ok, but for some reason 
tried to link kdevpythonlanguagesupport.so to a nonexistent python3.11 
library.

Installed a python3.11 which worked fine with kdevelop-python.

I assume that issue linking to a nonexistent python3.11 was not because 
of a problem with these changes.

---

Because I haven't contributed to KDE for many years now, it would take a 
lot of time to get the accounts and setups and learn how things are done 
now.

I hope you are able to review and commit if ok.

Attaching the patch.
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