Assume `git+` prefix when URLs end in `.git` (#5868)
## Summary
Right now, this applies _everywhere_, so the following also works:
```
pip install "elmer-circuitbuilder @ https://github.com/ElmerCSC/elmer_circuitbuilder.git"
```
I actually think that's ok?
Closes https://github.com/astral-sh/uv/issues/5866.
