[mlir][aarch64] XFAIL correctness.mlir

There are some discrepancies between the expected and the generated
output on AArch64 for this test. I reported these on GitHub:
  * https://github.com/llvm/llvm-project/issues/58531
I'm XFAILing this test as a temporary measure while this is being
investigated.

Differential Revision: https://reviews.llvm.org/D136458