Clarify the depth limit exception message

Author: wravery

src/SyntaxTree.cpp

@@ -700,8 +700,8 @@ struct ast_action<selection_set> : maybe_nothing
 		{
 			std::ostringstream oss;
 
-			oss << "Exceeded " << in.depthLimit()
-				<< " nested depth limit for https://spec.graphql.org/October2021/#SelectionSet";
+			oss << "Exceeded nested depth limit: " << in.depthLimit()
+				<< " for https://spec.graphql.org/October2021/#SelectionSet";
 
 			throw parse_error(oss.str(), in);
 		}

test/PegtlExecutableTests.cpp

@@ -220,7 +220,7 @@ TEST(PegtlExecutableCase, ParserDepthLimitExceeded)
 
 		const std::string_view error { ex.what() };
 		constexpr auto expected =
-			"GraphQL:4:3: Exceeded 2 nested depth limit for https://spec.graphql.org/October2021/#SelectionSet"sv;
+			"GraphQL:4:3: Exceeded nested depth limit: 2 for https://spec.graphql.org/October2021/#SelectionSet"sv;
 
 		EXPECT_TRUE(error == expected) << ex.what();