fix: Python examples/tests can be run from any directory

[timadye]

Python scripts in Examples/Python/tests and Examples/Scripts/Python should access config / data files from the acts source tree by using a path relative to the script's location (also in the source tree). They should not rely on the user's CWD being in the source tree.

This was already done in many cases. This PR fixes the remaining issues.

It is now possible to run pytest from the build directory as well as the source tree.

[paulgessinger]

LGTM!

[codecov]

Codecov Report

Merging #1074 (e89698b) into main (8b6bc7a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1074   +/-   ##
=======================================
  Coverage   48.56%   48.56%           
=======================================
  Files         341      341           
  Lines       17409    17409           
  Branches     8233     8233           
=======================================
  Hits         8454     8454           
  Misses       3195     3195           
  Partials     5760     5760           

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