Enable minimal testing with windows and macOS

[ssbarnea]

Due to the specific nature of how uv works, some minimal testing on Windows and MacOS would be needed.

Related: #193 #183
Related: astral-sh/uv#14239

[ssbarnea]

@gaborbernat I am unable to test this change because I cannot create branches in tox-uv itself and GHA pipeline changes run only on local PRs, not the ones from forks. Can you please give a hand with this? Thanks.

Here is PR I made with the same code on my branch https://github.com/ssbarnea/tox-uv/actions/runs/15777559807/job/44475364088?pr=2

If you want I can remove the pull_request_target from it. As you can see we have 3 broken Windows tests, which proves the need for platform testing. As a first stage I would probably add a conditional xfail to them to allow the testing to be abled, and fix them after. Sounds ok to you?

[gaborbernat]

If you want I can remove the pull_request_target from it. As you can see we have 3 broken Windows tests, which proves the need for platform testing. As a first stage I would probably add a conditional xfail to them to allow the testing to be abled, and fix them after. Sounds ok to you?

Ok.

[ssbarnea]

@gaborbernat I finally made it pass CI. I had to use "xfail" on some broken tests as they are not fixable by us. I fixed few minor issues with existing ones. Once this goes in we will be able to gradually address these bugs.

Please let me know what I need to change to close this one. Thanks.