Pin uv version installed by setup-uv (#22854)
## Summary
Same as
https://github.com/astral-sh/pyx/commit/94fc8813f513dbee1ab512d45d97bda2ce791fa8,
for the same reasons. This means that we avoid hitting the GitHub API to
figure out what version of uv the action should install, which seems to
fail pretty regularly (and is pretty annoying). The version pinned in
the GitHub workflow files should be auto-updated by Renovate (e.g.
https://github.com/astral-sh/uv/pull/17555)
## Test Plan
CI on this PR
