servo: Merge #13093 - Remove unneeded clone in the style system cache (from ashrko619:cache-element-classnames); r=nox

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #13089  (github issue number if applicable).

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Source-Repo: https://github.com/servo/servo
Source-Revision: db52d8a815a02be1f4f7e6270279235cec7005be

servo/components/style/matching.rs

@@ -388,7 +388,7 @@ fn have_same_class<E: TElement>(element: &E,
         candidate.class_attributes = Some(attrs)
     }
 
-    element_class_attributes == candidate.class_attributes.clone().unwrap()
+    element_class_attributes == *candidate.class_attributes.as_ref().unwrap()
 }
 
 // TODO: These re-match the candidate every time, which is suboptimal.