ci: updates for cargo-llvm-cov 0.5

[davidhewitt]

I think the Windows error in #2617 might be because xtask binary is running from the directory which cargo llvm-cov clean is trying to remove, so as an experiment am trying moving the coverage job to nox here:

[adamreichold]

I think the Windows error in #2617 might be because xtask binary is running from the directory which cargo llvm-cov clean is trying to remove

This seems to be indeed the case, but using --workspace also seems to make cargo-llvm-cov ignore the problem which might be the simpler fix?

[adamreichold]

Generally speaking, I think this does highlight a bit that keeping two xtask infrastructures working is additional work indeed. But that might also be me being grumpy due to running into the itertools regression while trying to understand the somewhat inscrutable cargo-llvm-cov error... (I have absolutely no preferences between the two xtask implementations though.)

[davidhewitt]

I'm thinking similarly; I was excited to use Rust for xtask but the added CI burden coupled with the existence of Python / nox for samples combined with MSRV preventing use of clap 3 means it's seeming easier to just fold back into nox. For now merged #2617 and will tidy this up another day.

[davidhewitt]

Superseded by #2634