Add interior-mutability suggestion to static_mut_refs

[JohnTitor]

Closes #151131
r? @estebank

I've skipped to expand catching below code as a mutable reference shouldn't be involved (maybe a new lint would be needed?):

static mut COUNTER: u64 = 0;
fn main() {
    unsafe { COUNTER = 1 };
}

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-bors]

☔ The latest upstream changes (presumably #153124) made this pull request unmergeable. Please resolve the merge conflicts.