Geant4 Fixes, main branch (2023.09.06.)
Unfortunately I was not careful enough with !1059 (merged).
But since I really wanted to build G4 itself in C++20 mode as well, I tested how hard it would be to force it to do so, and it wasn't too hard.
As long as I was doing this, I also improved a bit on how the !$%^& symbolic link would be handled in the G4 installation. Since our current setup for removing it as part of the post-install step is pretty fragile. (It doesn't work when not using -DCTEST_USE_LAUNCHERS=TRUE
for instance.) So I now rather opted for patching the G4 code not to create the symbolic link in the first place.