♻️ Recycle: schedule의 participantCount로 참여자 수 검증하도록 수정

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- 관련: #419

application/external-api-v2/src/main/java/com/namo/spring/application/external/api/schedule/usecase/MeetingScheduleUsecase.java

@@ -106,7 +106,7 @@ public void updateMeetingScheduleProfile(MeetingScheduleRequest.PatchMeetingSche
     public String getGuestInvitationUrl(Long scheduleId, SecurityUserDetails memberInfo) {
         Schedule schedule = scheduleManageService.getMeetingSchedule(scheduleId);
         scheduleManageService.validateAndGetOwnerParticipant(schedule, memberInfo.getUserId());
-        validateParticipantCount(participantManageService.getScheduleParticipantIds(schedule.getId()).size());
+        validateParticipantCount(schedule.getParticipantCount());
         return guestManageService.generateInvitationUrl(scheduleId);
     }