Inline a string used in lambda function to fix capture error

The string was referenced but not captured in the lambda, which causes
    a failure when compiling with MSVC.

    This issue was discovered by @loic-joly-sonarsource with a proposed fix
    in https://github.com/tensorflow/mlir/pull/22.

--

PiperOrigin-RevId: 247085897

mlir/lib/Transforms/Vectorization/VectorizerTestPass.cpp

@@ -145,13 +145,12 @@ static std::string toString(Operation *op) {
 }
 
 static NestedPattern patternTestSlicingOps() {
-  // Just use a custom op name for this test, it makes life easier.
-  constexpr auto kTestSlicingOpName = "slicing-test-op";
   using functional::map;
   using matcher::Op;
   // Match all operations with the kTestSlicingOpName name.
   auto filter = [](Operation &op) {
-    return op.getName().getStringRef() == kTestSlicingOpName;
+    // Just use a custom op name for this test, it makes life easier.
+    return op.getName().getStringRef() == "slicing-test-op";
   };
   return Op(filter);
 }