jaxlib build fixes. (#4066)
1. `wheel.pep425tags` has been removed as of
https://github.com/pypa/setuptools/pull/1829. Use the new
`packaging.tags` instead.
2. Add `--allow-downgrades` to cuda install command. I'm not sure this
is always necessary, but I ran into it, I'm guessing due to a cached
docker image.
