pw_sync_freertos: Fix regression in TimedThreadNotification

pwrev.dev/256695 contained a bug caused by the incorrect use of `auto`
with a reference type that created a copy of a thread notification's
NativeThreadNotification. Fix the issue by adding in explicit types.

Bug: 366374135
Change-Id: If259727acb223e415634e70ab4176591f811b32f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/256793
Lint: Lint 🤖 <[email protected]>
Pigweed-Auto-Submit: Kesavan Yogeswaran <[email protected]>
Commit-Queue: Kesavan Yogeswaran <[email protected]>
Docs-Not-Needed: Kesavan Yogeswaran <[email protected]>
Presubmit-Verified: CQ Bot Account <[email protected]>
Reviewed-by: Prabhu Karthikeyan Rajasekaran <[email protected]>
Reviewed-by: Alan Rosenthal <[email protected]>

pw_sync_freertos/timed_thread_notification.cc

@@ -61,7 +61,7 @@ bool TimedThreadNotification::try_acquire_until(
   PW_DCHECK(xTaskNotifyStateClear(nullptr) == pdFALSE);
 
   {
-    auto handle = native_handle();
+    native_handle_type handle = native_handle();
     std::lock_guard lock(handle.shared_spin_lock);
     const bool notified = handle.notified;
     // Don't block if we've already reached the specified deadline time.
@@ -87,7 +87,7 @@ bool TimedThreadNotification::try_acquire_until(
     }
   }
 
-  auto handle = native_handle();
+  native_handle_type handle = native_handle();
   std::lock_guard lock(handle.shared_spin_lock);
   // We need to clear the thread notification state in case we were
   // notified after timing out but before entering this critical section.