Integration test uv_build package (#12058)
I somehow missed running an actual integration test of the PEP 517 API
in CI and the python shim was using the old uv CLI interface still.
The tests include pip, uv and `python -m build`. They must be a in CI
job since we can't depend on the Python package in the Rust tests (we
only get the binary in `cargo test`, not the `uv_build` wheel).
