Nightly source tarballs don't have tests/ directory

[aeubanks]

Downloading the nightly sources from https://static.rust-lang.org/dist/rustc-nightly-src.tar.gz, there's no tests directory.

$ cat git-commit-info 
333ee6c466972185973d5097f8b5fb0f9fb13fa5
333ee6c46
2023-01-18

presumably something wasn't updated after the big src/test -> tests commit

[albertlarsan68]

@rustbot label +T-infra