actually warn on web workers

embassy-time/src/driver_wasm.rs

@@ -45,13 +45,20 @@ embassy_time_driver::time_driver_impl!(static DRIVER: TimeDriver = TimeDriver {
     alarms: UninitCell::uninit(),
 });
 
+#[cfg(feature = "panic_on_webworker")]
+thread_local!{
+    static CHECK_THREAD: Once = Once::new();
+}
+
 impl TimeDriver {
     fn ensure_init(&self) {
         self.once.call_once(|| unsafe {
             self.alarms.write(Mutex::new([ALARM_NEW; ALARM_COUNT]));
-			#[cfg(feature = "panic_on_webworker")]
-            assert!(!is_web_worker_thread(), "Timer currently has issues on Web Workers: https://github.com/embassy-rs/embassy/issues/3313");
         });
+        #[cfg(feature = "panic_on_webworker")]
+        CHECK_THREAD.with(|val| val.call_once(|| {
+            assert!(!is_web_worker_thread(), "Timer currently has issues on Web Workers: https://github.com/embassy-rs/embassy/issues/3313");
+        }));
     }
 }