coverage: Disable the zombie MC/DC tests until they support LLVM 19

[Zalathar]

Currently these tests only run against LLVM 18, but the default is now LLVM 19, which makes them very tricky to bless. Since #126733 is going to drop support for MC/DC in LLVM 18 anyway, it's easier to just completely disable the tests until that PR fixes them.

(For context, MC/DC is currently unstable anyway, and LLVM's MC/DC APIs have changes between 18 and 19, so supporting both would be an unnecessary headache.)

r? jieyouxu

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[Zalathar]

I was originally hoping to avoid this by just approving #126733 myself, but that PR turns out to have bit-rotted slightly and needs a rebase.

[Zalathar]

@jieyouxu I believe you were annoyed by these tests recently so you have some context for why they should be disabled.

[jieyouxu]

Thanks! Yeah I ran into this when trying to see if I can bless coverage tests for #130766 locally. The CI llvm got bumped to llvm 19, but these tests require llvm 18, and then becomes a PITA to bless.

[jieyouxu]

@bors r+ rollup

[bors]

📌 Commit 729c140 has been approved by jieyouxu

It is now in the queue for this repository.

[Zalathar]

Pulling this out of the queue because #126733 has been updated, so if that lands then this change becomes unnecessary.

@bors r-

[bors]

☔ The latest upstream changes (presumably #126733) made this pull request unmergeable. Please resolve the merge conflicts.

[Zalathar]

Obsoleted by #126733.