GeoModel version bumped to 5.4.0

This was implemented using CMake overriders in build_externals.sh scripts.

FYI @akraszna. Hopefully, this will not interfere with the 2.1.13 tag of atlasexternals when you create an MR switching Athena main to it.

Tag: @nstyles

P.S. The new GeoModel release does not contain interface changes that can affect client code in Athena. Setting the full-build label just in case