Auto merge of #26998 - gterzian:improve_task_cancelling, r=jdm

Use a stronger atomic guarantee when cancelling tasks

<!-- Please describe your changes on the following line: -->

In the context of https://github.com/servo/servo/issues/22507

Note that the "other side" of these operations is at 0b61cfc3ae/components/script/task.rs (L102)

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

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

components/script/dom/window.rs

@@ -399,7 +399,7 @@ impl Window {
             let flag = ignore_flags
                 .entry(task_source_name)
                 .or_insert(Default::default());
-            flag.store(true, Ordering::Relaxed);
+            flag.store(true, Ordering::SeqCst);
         }
     }
 
@@ -1431,7 +1431,7 @@ impl Window {
                 .entry(task_source_name)
                 .or_insert(Default::default());
             let cancelled = mem::replace(&mut *flag, Default::default());
-            cancelled.store(true, Ordering::Relaxed);
+            cancelled.store(true, Ordering::SeqCst);
         }
     }
 
@@ -1444,7 +1444,7 @@ impl Window {
             .entry(task_source_name)
             .or_insert(Default::default());
         let cancelled = mem::replace(&mut *flag, Default::default());
-        cancelled.store(true, Ordering::Relaxed);
+        cancelled.store(true, Ordering::SeqCst);
     }
 
     pub fn clear_js_runtime(&self) {