Two changes to `redundant_guards`:
- Lint float literals. We used to do that before but that was changed in
#11305 because at the time there was a future compat warning and it was
planned to make pattern matching floats a hard error.
In rust-lang/rust#116284 it was decided to actually remove the lint and
only make matching `NAN` specifically a hard error. The `NAN` part isn't
relevant/important here because this PR only changes what literals are
warned and `f64::NAN` isn't a literal, but I've added a test anyway to
make sure we continue to not lint there.
- Don't lint CStr literals because that can't be a pattern right now
(fixes#13681)
changelog: none
8698c31f88