fix: 참여자 목록 조회 API에서 totalCount 반환하지 않는 이슈 해결 (#400)

backend/src/main/java/com/zzang/chongdae/offeringmember/service/dto/ParticipantCountResponseItem.java

@@ -5,6 +5,6 @@
 public record ParticipantCountResponseItem(int currentCount, int totalCount) {
 
     public ParticipantCountResponseItem(OfferingEntity offering) {
-        this(offering.getCurrentCount(), offering.getCurrentCount());
+        this(offering.getCurrentCount(), offering.getTotalCount());
     }
 }