Do not emit `-Winaccessible-code` warnings when the pattern-match checker would warn as well
https://discourse.haskell.org/t/inaccessible-vs-redundant-warnings-in-gadt-pattern-matching/8952 had one more user confused by the apparent redundancy of -Winaccessible-code
warnings with those of the pattern-match checker.
In #19428 I proposed to deprecate -Winaccessible-code
for this reason, but @RyanGlScott correctly pointed out that there are inaccessible code warnings that have no equivalent in the pattern-match checker.
So in this ticket, I instead propose not to generate -Winaccessible-code
warnings inside patterns.