Use uv for running tests

[antonpirker]

This is an experiment to try to use uv for our CI running the tests and see if it speeds up things.

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[antonpirker]

Ok, sometimes it is really way faster like with our web frameworks 2 test suite:

web frameworks 2:
normal: https://github.com/getsentry/sentry-python/actions/runs/8598128406/job/23558323415?pr=2690
with uv: https://github.com/getsentry/sentry-python/actions/runs/8602095050/job/23570859665?pr=2943

But for example the Django tests are not faster at all. But not sure If I am just holding it wrong:

web frameworks 1:
normal: https://github.com/getsentry/sentry-python/actions/runs/8598128398/job/23558330541?pr=2690
with uv: https://github.com/getsentry/sentry-python/actions/runs/8602095042/job/23570870189?pr=2943