Suggestion: cargo update before msrv's cargo check

[Alex Kazik]

In my example I added the dependency trybuild 1.0.85 while running on stable (1.73.0).
And all tests work fine.
The msrv check on github however does fail with:

Run cargo check
  cargo check
  shell: /usr/bin/bash -e {0}
  env:
    CARGO_INCREMENTAL: 0
    CARGO_TERM_COLOR: always
    Updating crates.io index
error: failed to select a version for the requirement `once_cell = "^1.9.0"`
candidate versions found which didn't match: 1.17.2, 1.17.1, 1.17.0, ...
location searched: crates.io index
required by package `trybuild v1.0.85`
    ... which satisfies dependency `trybuild = "^1.0.85"` (locked to 1.0.85) of package `private v0.0.0 (/home/runner/work/private/private)`
Error: Process completed with exit code 101.

As it turns out: once_cell 1.18.0 was added in the Cargo.lock, which is not compatible with the rust 1.58.1 (my msrv).

Running a cargo update before cargo check does the trick, as it downgrades it:

Run cargo update
    Updating crates.io index
    Updating once_cell v1.18.0 -> v1.17.2

Or are you running locally the msrv compiler, if yes simply close this request.
I'm happy to write a PR if this is wanted.

Edit: maybe it's not as good idea as I thought because it takes like 5 minutes to do the update (every run).

[Jon Gjengset]

Yeah, it's actually intentional that we don't run cargo update except for the scheduled set of jobs — it ensures that all the jobs test the same dependency closure, and that updates are handled more explicitly. It also (at least in theory) better allows cache sharing between jobs. So I'd like to keep it this way :)