对话题改为固定高度

src/views/exercise_questions/create/components/exercises/DialogueQuestion.vue

@@ -491,7 +491,7 @@ export default {
       }
 
       .image img {
-        max-height: 180px;
+        height: 180px;
         border-radius: 8px;
       }
     }

src/views/exercise_questions/preview/DialoguePreview.vue

@@ -257,7 +257,7 @@ export default {
       }
 
       .image img {
-        max-height: 180px;
+        height: 180px;
         border-radius: 8px;
       }
     }