[mlir][test] Fix -Wsign-compare in TestDialect.cpp (NFC)

llvm-project/mlir/test/lib/Dialect/Test/TestDialect.cpp:597:31:
error: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'int64_t' (aka 'long') [-Werror,-Wsign-compare]
  if (getVarOperands().size() != expectedNumOperands)
      ~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~
1 error generated.

Author: DamonFool

mlir/test/lib/Dialect/Test/TestDialect.cpp

@@ -594,7 +594,7 @@ LogicalResult CompareOp::verify() {
         "'compose' not supported when 'lhs_map' or 'rhs_map' is present");
   int64_t expectedNumOperands = getLhsMap() ? getLhsMap()->getNumInputs() : 1;
   expectedNumOperands += getRhsMap() ? getRhsMap()->getNumInputs() : 1;
-  if (getVarOperands().size() != expectedNumOperands)
+  if (getVarOperands().size() != size_t(expectedNumOperands))
     return emitOpError("expected ")
            << expectedNumOperands << " operands, but got "
            << getVarOperands().size();