Auto merge of #12277 - ConnorGBrewster:network_listener_cancellable, r=Manishearth

Make network listener runnable cancellable

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This keeps scripts from executing after its script thread has been shut down.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [x] These changes fix (maybe) #12048 (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12277)
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components/script/dom/window.rs

@@ -949,7 +949,7 @@ impl Window {
         self.current_state.set(WindowState::Zombie);
         *self.js_runtime.borrow_mut() = None;
         self.browsing_context.set(None);
-        self.ignore_further_async_events.store(true, Ordering::Relaxed);
+        self.ignore_further_async_events.store(true, Ordering::SeqCst);
     }
 
     /// https://drafts.csswg.org/cssom-view/#dom-window-scroll