[mlir][linalg][transform][python] Verify modules in mix-in tests.

[ingomueller-net]

Summary

The tests of the mix-in classes of the Python bindings currently passed
even if the ops constructed by the mix-ins under test failed to verify.
This is because the assembled IR is still printed in generic form even
if it does not verify, and the CHECK statements are formulated in such
a lenient way that they also match that generic form. This patch adds
explicit verification to the decorator that is used for all test
functions.

mlir/test/python/dialects/transform_structured_ext.py

 # RUN: %PYTHON %s | FileCheck %s
 
 from mlir.ir import *
 from mlir.dialects import transform
 from mlir.dialects import pdl
 from mlir.dialects.transform import structured
 from mlir.dialects.transform import pdl as transform_pdl
 
 
 def run(f):
     with Context(), Location.unknown():
         module = Module.create()
         with InsertionPoint(module.body):
             print("\nTEST:", f.__name__)
             f()
+        module.operation.verify()
         print(module)
     return f
 
 
 @run
 def testDecompose():
     sequence = transform.SequenceOp(
         transform.FailurePropagationMode.PROPAGATE, [], pdl.OperationType.get()