Bug 1767996 - Apply readability-make-member-function-const on dom/html r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D145627

dom/html/HTMLImageElement.cpp

@@ -105,7 +105,7 @@ class ImageLoadTask final : public MicroTaskRunnable {
     return global && global->IsInSyncOperation();
   }
 
-  bool AlwaysLoad() { return mAlwaysLoad; }
+  bool AlwaysLoad() const { return mAlwaysLoad; }
 
  private:
   ~ImageLoadTask() = default;