Revert "refactor: 可読性のため一部でArray.prototype.atを使うように" (#115)

* Revert "refactor: 可読性のため一部で`Array.prototype.at`を使うように (#11274)"

This reverts commit 2b6dbd4fcb.

* Apply suggestions from code review

---------

Co-authored-by: okayurisotto <okayurisotto@proton.me>

packages/backend/src/queue/processors/ExportBlockingProcessorService.ts

@@ -72,7 +72,7 @@ export class ExportBlockingProcessorService {
 					break;
 				}
 
-				cursor = blockings.at(-1)?.id ?? null;
+				cursor = blockings[blockings.length - 1].id;
 
 				for (const block of blockings) {
 					const u = await this.usersRepository.findOneBy({ id: block.blockeeId });