fix(test): use module-exported names in get_scheduler() composition check

The final assertion named ex::__as_awaitable::__completes_inline, which is not
part of the stdexec module's exported surface: the clang-trunk modules build
rejected the name ("must be declared before it is used") and nvc++ could not
resolve the namespace at all ("name followed by '::' must be a class or
namespace name"), failing 4 CI configurations.

Replace it with assertions on the exported per-tag concept: the composition's
set_value_t completes inline (let_value forwards read_env's inline value
completion), while its set_stopped_t does not (the nested schedule()
completes asynchronously), so a co_await on it must not be treated as
completing inline. Both hold on current main and fail at 482c260.

Author: alwaysprince05

test/stdexec/queries/test_get_completion_behavior.cpp

@@ -84,5 +84,18 @@ inline constexpr auto __reschedule = [](auto __sch)
 };
 inline constexpr auto __reschedule_on_current = ex::get_scheduler() | ex::let_value(__reschedule);
 
-static_assert(
-  !ex::__as_awaitable::__completes_inline<decltype(__reschedule_on_current), ex::env<>>);
+// For co_await, a sender is treated as completing inline only if _all_ of its
+// completion tags complete inline (see __as_awaitable::__completes_inline). The
+// nested schedule(sch) does not complete inline for set_stopped_t, so the
+// composition must not be classified as completing inline. We check the stopped
+// tag directly; the value tag of the composition _does_ complete inline
+// (let_value forwards read_env's inline value completion), so that is pinned
+// here as well. This check uses only names exported by the stdexec module: the
+// __as_awaitable namespace is not part of the module's public surface, and
+// naming it fails the modular and nvc++ configurations.
+static_assert(ex::__completes_inline<ex::set_value_t,
+                                     ex::env_of_t<decltype(__reschedule_on_current)>,
+                                     ex::env<>>);
+static_assert(!ex::__completes_inline<ex::set_stopped_t,
+                                      ex::env_of_t<decltype(__reschedule_on_current)>,
+                                      ex::env<>>);