508bb36f8b
In CLI mode, SetGitBackend() is never called so GetGitBackend() returns
nullptr. GetRepositoryForFile(), CreateBranch(), and RemoveVCS() all
called GetGitBackend()->method() unconditionally, causing a SIGSEGV when
a schematic containing ${VCSHASH} or ${VCSSHORTHASH} text variables is
loaded via kicad-cli jobset run.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/23214