tests: adapt GTest smoke-tests to MockDDS annotated payload format (seq:payload)

Lts/DDS/DdsUnitTestsPlaceholder/ddsFunctionTopicTests_gtest.cpp

@@ -13,5 +13,8 @@ TEST(FunctionTopicSmokeGTest, MockDDSTopicAsSignal) {
   MockDDS::clear_all();
   MockDDS::publish("func/topic", "evt:1");
   auto val = MockDDS::take_last("func/topic");
-  EXPECT_EQ(val, "evt:1");
+  auto payload = val.substr(val.find(':') + 1);
+  EXPECT_EQ(payload, "evt:1");
+  auto seq = std::stoul(val.substr(0, val.find(':')));
+  EXPECT_EQ(seq, 1UL);
 }