[VPlan] Update check line in verifier unit test w/o assertions.

Should fix failures with assertions disabled, including
https://lab.llvm.org/buildbot/#/builders/2/builds/24015.

Author: fhahn

llvm/unittests/Transforms/Vectorize/VPlanVerifierTest.cpp

@@ -174,8 +174,9 @@ TEST_F(VPVerifierTest, VPPhiIncomingValueDoesntDominateIncomingBlock) {
                "  EMIT vp<%1> = phi [ vp<%2>, preheader ]",
                ::testing::internal::GetCapturedStderr().c_str());
 #else
-  EXPECT_STREQ("Use before def!\n",
-               ::testing::internal::GetCapturedStderr().c_str());
+  EXPECT_STREQ("Incoming def at index 0 does not dominate incoming block!\n" ::
+                   testing::internal::GetCapturedStderr()
+                       .c_str());
 #endif
 #endif
 }