[bazel] Enable layering_check for MLIR test directory

This would have enabled me to notice the MLIR test file needed updating too, preventing the test file of 2074eef5db from being necessary.

layering_check is already enabled in mlir/BUILD.bazel. I don't know why I didn't see the other breakage there.

Differential Revision: https://reviews.llvm.org/D118125

utils/bazel/llvm-project-overlay/mlir/test/BUILD.bazel

@@ -6,6 +6,7 @@ load("//mlir:tblgen.bzl", "gentbl_cc_library", "td_library")
 
 package(
     default_visibility = ["//visibility:public"],
+    features = ["layering_check"],
     licenses = ["notice"],
 )