Update to support 2022-07-11 `rustc_middle`

[fw-immunant]

This will want either a docker redeploy with the new rust-toolchain file or a change to use rust-toolchain.toml so rustup can add the required components dynamically.

[kkysen]

This is causing some weird compile errors, both in CI and locally (but different ones). Locally, I'm also seeing this from cargo doc:

error[E0308]: mismatched types
   --> /home/kkysen/.cargo/registry/src/github.com-1ecc6299db9ec823/semver-1.0.10/src/lib.rs:525:29
    |
525 |     pub const EMPTY: Self = "";
    |                             ^^ expected struct `BuildMetadata`, found `&str`

error[E0308]: mismatched types
   --> /home/kkysen/.cargo/registry/src/github.com-1ecc6299db9ec823/semver-1.0.10/src/lib.rs:502:29
    |
502 |     pub const EMPTY: Self = "";
    |                             ^^ expected struct `Prerelease`, found `&str`

For more information about this error, try `rustc --explain E0308`.

[kkysen]

Ah, the CI errors are from old rustup component add rust-src rustc-dev. I'm working right now on the rust-toolchain.toml fix, which should solve that (so that CI passes, but it'll still have to download components every time until we update the docker containers).

[kkysen]

The semver doc compile error is our cargo dependency causing issues again. I'll update it. We really should get rid of cargo, though. It's caused many, many issues by now.

[fw-immunant]

I'll rebase.

[kkysen]

Superceded by #595.