refactor join PR리뷰 관해 업데이트

- leftjoin -> join으로 수정
join으로 수정하여도 shareProposalLetter는 반드시 1개 이상의 공유 편지가 존재한다.
null 값이 들어갈 수 없기에 이부분은 join으로 수정.

Author: HeoJeongHyeon

src/main/java/io/crops/warmletter/domain/share/repository/ShareProposalRepositoryImpl.java

@@ -79,7 +79,7 @@ public ShareProposalDetailResponse findShareProposalDetailById(Long shareProposa
                 .from(SHARE_PROPOSAL)
                 .join(REQUESTER_MEMBER).on(SHARE_PROPOSAL.requesterId.eq(REQUESTER_MEMBER.id))
                 .join(RECIPIENT_MEMBER).on(SHARE_PROPOSAL.recipientId.eq(RECIPIENT_MEMBER.id))
-                .leftJoin(shareProposalLetter).on(SHARE_PROPOSAL.id.eq(shareProposalLetter.proposalId))
+                .join(shareProposalLetter).on(SHARE_PROPOSAL.id.eq(shareProposalLetter.proposalId))
                 .leftJoin(letter).on(shareProposalLetter.letterId.eq(letter.id))
                 .leftJoin(letterWriterMember).on(letter.writerId.eq(letterWriterMember.id))
                 .leftJoin(letterReceiverMember).on(letter.receiverId.eq(letterReceiverMember.id))