fix: vecgeom ~geant4 to avoid circular dependency

Author: wdconinc

spack-environment/packages.yaml

@@ -536,7 +536,7 @@ packages:
   vecgeom:
     require:
     - '@1.2.11'
-    - cxxstd=20 +gdml +geant4 +root
+    - cxxstd=20 +gdml ~geant4 +root
   xerces-c:
     require:
     - cxxstd=20