[#23] fix: 코드 위치 수정

Co-authored-by: 서정준 <51807128+chance0523@users.noreply.github.com>

src/test/java/com/study/realworld/user/service/UserServiceTest.java

@@ -217,11 +217,9 @@ void save_validateDuplicateUser_exception() {
                 .image(IMAGE)
                 .build();
 
+        // when
         when(userRepository.findByEmail(anyString()))
                 .thenReturn(Optional.ofNullable(user));
-
-        // when
-
         // then
         assertThrows(DuplicateKeyException.class, () -> userService.save(request));
     }