fix context sentences in YAML to ensure vocab emphasis

docs/howtostudykorean/theme/04-shopping.md

@@ -425,10 +425,10 @@ vocabulary:
       notes: |
         The examples below use the related noun form 환불 (refund) with 되다/받다, which is very common in everyday speech alongside the plain verb 환불하다.
       examples:
-        - ko: "환불은 안 됩니다"
-          en: "No refund"
-        - ko: "사과가 다 상해서 환불을 받아야 돼요"
-          en: "I need to get a refund because all the apples have gone bad"
+        - ko: "**환불**은 안 됩니다"
+          en: "No **refund**"
+        - ko: "사과가 다 상해서 **환불**을 받아야 돼요"
+          en: "I need to get a **refund** because all the apples have gone bad"
 
     - ko: "비교하다"
       en: "to compare"