fix: 기획 변경에 따른 편지 목록 조회 로직 수정 #3

src/main/java/com/nexters/covid/letter/service/LetterService.java

@@ -39,6 +39,7 @@ public List<LetterResponse> findLettersByEmail(String email, boolean unposted) {
     }
     return letterRepository.findLettersByEmailOrderByCreatedDateDesc(email)
         .stream()
+        .filter(l -> !l.unpostedSendOption())
         .map(LetterResponse::new)
         .collect(Collectors.toList());
   }