testsuite, coroutines : Fix a bad testcase [PR96504].

Where possible (i.e. where that doesn't alter the intent of a test) we
use a suspend_always as the final suspend and a test that the coroutine
was 'done' to check that the state machine had terminated correctly.

Sometimes, filed PRs have 'suspend_never' as the final suspend expression
and that needs to be changed to match the testsuite style.  This is one
I missed and means that the call to 'done()' on the handle is made to an
already-destructed coroutine.  Surprisngly, thAt  didn't actually trigger
a failure until glibc 2-32.

Fixed by changing the final suspend to be 'suspend_always'.

gcc/testsuite/ChangeLog:

	PR c++/96504
	* g++.dg/coroutines/torture/pr95519-05-gro.C: Use suspend_always
	as the final suspend point so that we can check that the state
	machine has reached the expected point.

gcc/testsuite/g++.dg/coroutines/torture/pr95519-05-gro.C

@@ -5,7 +5,7 @@
 struct pt_b
 {
   std::suspend_always initial_suspend() const noexcept { return {}; }
-  std::suspend_never final_suspend() const noexcept { return {}; }
+  std::suspend_always final_suspend() const noexcept { return {}; }
   constexpr void return_void () noexcept {};
   constexpr void unhandled_exception() const noexcept {}
 };