[`pylint`] Do not offer fix for raw strings (`PLE251`) (#16132)
## Summary
Resolves #13294, follow-up to #13882.
At #13882, it was concluded that a fix should not be offered for raw
strings. This change implements that. The five rules in question are now
no longer always fixable.
## Test Plan
`cargo nextest run` and `cargo insta test`.
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Co-authored-by: Micha Reiser <micha@reiser.io>
