Update LArCustomSolidExtension to git url without redirect
I run into issues when trying to build the ATLAS externals in a singularity container. Here, the recursive clone step in CMake, git has to follow a redirect from
https://gitlab.cern.ch/SolidExtensions/LArCustomSolidExtension
to https://gitlab.cern.ch/SolidExtensions/LArCustomSolidExtension.git
which fails, I believe due to the singularity environment.
I believe updating the submodule git url to the redirect target should be safe to do.
Edited by Paul Gessinger