fix: 누락된 Transactional 옵션 추가

Author: yuseok0215

src/main/java/bitnagil/bitnagil_backend/report/service/ReportService.java

@@ -46,7 +46,7 @@ public long registerReport(User user, ReportRegisterRequest request) {
     }
 
     // 제보 전체 목록 조회
-    @Transactional
+    @Transactional(readOnly = true)
     public ReportInfoResponse getAllReportInfo(User user) {
         List<Report> reports = reportRepository.findByUser(user);