fix: Relative path of MuonChamber.gdml independend of working direc…

…tory (#2152)

Now the script finds `MuonChamber.gdml` even when `mockupbuilder.py` is
run from outside its folder.

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>
Co-authored-by: Andreas Stefl <stefl.andreas@gmail.com>

Examples/Python/python/acts/examples/mockupbuilder.py

@@ -1,3 +1,5 @@
+import os
+
 import acts
 import acts.examples.geant4 as actsG4
 
@@ -18,8 +20,10 @@
 mockupChamberConfigOuter.SensitiveNames = ["Outer_Skin"]
 mockupChamberConfigOuter.PassiveNames = ["xx"]
 
-mockupConfig.gdmlPath = (
-    "../../../../Detectors/MuonSpectrometerMockupDetector/MuonChamber.gdml"
+dirOfThisScript = os.path.dirname(__file__)
+mockupConfig.gdmlPath = os.path.join(
+    dirOfThisScript,
+    "../../../../Detectors/MuonSpectrometerMockupDetector/MuonChamber.gdml",
 )
 mockupConfig.NumberOfSectors = 8