Don't lint CStr literals, do lint float literals in redundant_guards

[y21]

Two changes to redundant_guards:

• Lint float literals. We used to do that before but that was changed in [redundant_guards]: don't lint on float literals #11305 because at the time there was a future compat warning and it was planned to make pattern matching floats a hard error.

  In make matching on NaN a hard error, and remove the rest of illegal_floating_point_literal_pattern 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 redundant_guards suggests change that doesn't compile for matching on CStr #13681)

changelog: none

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[Centri3]

Thanks 👍