Update rust-analyzer config checkOnSave -> check

[lukas-code]

This setting was renamed in rust-lang/rust-analyzer#13799.

Turns out that was the reason my analyzer hasn't been working recently.

[flodiebold]

The old config keys should still work though, right @Veykril ?

[Veykril]

Ye we should still be accepting the old key here 🤔

[lukas-code]

This might be a rust-analyzer bug then. I just double checked with r-a default settings and the old config doesn't work, but with this patch it works.

r-a version: 0.4.1371-standalone

[Veykril]

I'll look into it.

[Veykril]

Found the problem rust-lang/rust-analyzer#13980, we should still update the dev-guide to be up to date, but ideally let this PR sit for a bit, since I assume some people that work on rustc might be using the rust-analyzer shipped as a stable rustup component which doesn't have the updated configs yet.

[clubby789]

The suggested config has been moved into bootstrap here.

[lukas-code]

I'll close this per #1562 (comment). The config in the rust repo should still be updated eventually.