Activate LLVM tests for Windows in CI

[lukewilliamboswell]

No description provided.

[lukewilliamboswell]

@Anton-4, no rush with this but I think we might need to update something on the CI machine for this, or potentially look at optimising things if the tests are too large/slow etc.

[Anton-4]

Hmm, do you think the test failure will be fixed by updating a dependency @lukewilliamboswell?

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