[mlir] Skip invalid test on big endian platform (s390x) (#80246)

The buildbot test running on s390x platform keeps failing since [this
time](https://lab.llvm.org/buildbot/#/builders/199/builds/31136). This
is because of the dependency on the endianness of the platform. It
expects the format invalid in the big endian platform (s390x). We can
simply skip it.

See: https://discourse.llvm.org/t/mlir-s390x-linux-failure/76695