fixed git submodule bug when using relative paths

[Choudhry18]

Summary

This fixes installations using git which involved submodules declared through relative paths, fixes #9822 .

Test Plan

I did testing using a private gitlab server that I was running locally, to recreate the issue. I have also added tests that involve installing from a repository that I created on my GitHub. Adding that repository and it's accompanying submodule to uv-test (I see there is already a repository - uv_submodule_pypackage that tests submodule installation but that doesn't use relative path) should work.