mod::테스트코드 수정

Author: jjjh02

ontime-back/src/test/java/devkor/ontime_back/controller/ScheduleControllerTest.java

@@ -212,7 +212,7 @@ void getPreparation_success() throws Exception {
         when(scheduleService.getPreparations(userId, scheduleId)).thenReturn(mockPreparations);
 
         // when & then
-        mockMvc.perform(get("/schedules/{scheduleId}/preparation", scheduleId)
+        mockMvc.perform(get("/schedules/{scheduleId}/preparations", scheduleId)
                         .header("Authorization", "Bearer test-token")
                         .contentType(MediaType.APPLICATION_JSON))
                 .andExpect(status().isOk())  // HTTP 200 확인