fix(db): make remaining blog migrations idempotent

db/migrations/V024__UpdateBlogsWithLatestTemplate.sql

@@ -156,7 +156,7 @@ $$,
   1,
   true,
   NOW()
-);
+) ON CONFLICT (slug) DO NOTHING;
 
 -- 2. 이번달 부가가치세 신고
 INSERT INTO blog_posts (title, slug, content, category_id, is_published, created_at)
@@ -311,7 +311,7 @@ $$,
   1,
   true,
   NOW()
-);
+) ON CONFLICT (slug) DO NOTHING;
 
 -- 3. 프리랜서를 위한 종합소득세 신고
 INSERT INTO blog_posts (title, slug, content, category_id, is_published, created_at)
@@ -462,4 +462,5 @@ $$,
   1,
   true,
   NOW()
-);
+) ON CONFLICT (slug) DO NOTHING;
+