Use uv more in CI workflows (#20968)
## Summary
More dogfooding of our own tools.
I didn't touch the build-binaries workflow (it's scary) or the
publish-docs workflow (which doesn't run on PRs) or the ruff-lsp job in
the ci.yaml workflow (ruff-lsp is deprecated; it doesn't seem worth
making changes there).
## Test Plan
CI on this PR
