[MLIR][Python] fix python_test.py to not use is for type hint (#160718)

`is` causes the asserts to fail when the return hint is interpreted as 
`OpResult | OpResultList | test.SameVariadicResultSizeOpVFV`

Author: makslevental

mlir/test/python/dialects/python_test.py

@@ -904,7 +904,7 @@ def types(lst):
 
             assert (
                 typing.get_type_hints(test.same_variadic_result_vfv)["return"]
-                is Union[OpResult, OpResultList, test.SameVariadicResultSizeOpVFV]
+                == Union[OpResult, OpResultList, test.SameVariadicResultSizeOpVFV]
             )
             assert (
                 type(test.same_variadic_result_vfv([i[0], i[1]], i[2], [i[3], i[4]]))
@@ -992,7 +992,7 @@ def types(lst):
 
             assert (
                 typing.get_type_hints(test.results_variadic)["return"]
-                is Union[OpResult, OpResultList, test.ResultsVariadicOp]
+                == Union[OpResult, OpResultList, test.ResultsVariadicOp]
             )
             assert type(test.results_variadic([i[0]])) is OpResult
             op_res_variadic = test.ResultsVariadicOp([i[0]])
@@ -1003,7 +1003,7 @@ def types(lst):
             assert type(op_res_variadic.res) is OpResultList
 
 
-# CHECK-LABEL: TEST: testVariadicAndNormalRegion
+# CHECK-LABEL: TEST: testVariadicAndNormalRegionOp
 @run
 def testVariadicAndNormalRegionOp():
     with Context() as ctx, Location.unknown(ctx):