Silence some Clang warnings about unused return values in tests.

test/async_mutex_tests.cpp

@@ -72,7 +72,7 @@ TEST_CASE("multiple lockers")
 		// We'lll now queue up another one before releasing any more waiters
 		// to test the code-path that looks at the newly queued waiter list
 		// when the cache of waiters is exhausted.
-		co_await cppcoro::when_all_ready(f(d), check2());
+		(void)co_await cppcoro::when_all_ready(f(d), check2());
 	};
 
 	cppcoro::sync_wait(cppcoro::when_all_ready(

test/task_tests.cpp

@@ -65,7 +65,7 @@ TEST_CASE("awaiting task that completes asynchronously")
 
 		CHECK(!reachedBeforeEvent);
 
-		co_await cppcoro::when_all_ready(
+		(void)co_await cppcoro::when_all_ready(
 			[&]() -> cppcoro::task<>
 			{
 				co_await t;