Auto merge of #11974 - ConnorGBrewster:load_blocker_drop_debug_assert, r=asajeffrey

Change load blocker drop assert to debug_assert

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This was causing some crashes for myself and @glennw in browser.html
I will open an issue for this to be investigated later.

---
<!-- 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
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because `assert` to `debug_assert`

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components/script/document_loader.rs

@@ -86,7 +86,7 @@ impl LoadBlocker {
 impl Drop for LoadBlocker {
     fn drop(&mut self) {
         if !thread::panicking() {
-            assert!(self.load.is_none());
+            debug_assert!(self.load.is_none());
         }
     }
 }