[MLIR] Restore dropped error message to fix test failures from PR llvm#160331

PR llvm#160331 introduced a mistake that removed the error message for generate-runtime-verification
pass, leading to two test failures during `check-mlir` build.

This patch restores the missing error message, resolving the failures. Verified locally.

Fixes post-merge regression from: llvm#160331

Author: HanchengWu

mlir/lib/Transforms/GenerateRuntimeVerification.cpp

@@ -51,7 +51,7 @@ class DefaultErrMsgGenerator {
     stream << "ERROR: Runtime op verification failed\n";
     if (vLevel == 1) {
       op->print(stream, state);
-      stream << "\n";
+      stream << "\n" << msg;
     }
     stream << "^\nLocation: ";
     op->getLoc().print(stream);