This commit was cherry-picked from Fedora rawhide
<79d75fdcdd?branch=rawhide>.
This fixes the following test failure.
```
1) Failure:
TestGemSourceGit#test_checkout_submodules [/builddir/build/BUILD/ruby-3.0.4/test/rubygems/test_gem_source_git.rb:72]:
fatal: transport 'file' not allowed
fatal: clone of '/builddir/build/BUILD/ruby-3.0.4/tmp/test_rubygems_20230627-4031323-yppcjj/git/b' into submodule path '/builddir/build/BUILD/ruby-3.0.4/tmp/test_rubygems_20230627-4031323-yppcjj/git/a/b' failed
```
Resolves: rhbz#2173531
Jun Aruga