refactor(backend): 存在確認のfindOneByをexistに置き換え (#11224)

* refactor(backend): 存在確認の`findOneBy`を`exist`に置き換え

* cleanup

packages/backend/src/server/api/endpoints/admin/promo/create.ts

@@ -50,9 +50,9 @@ export default class extends Endpoint<typeof meta, typeof paramDef> {
 				throw e;
 			});
 
-			const exist = await this.promoNotesRepository.findOneBy({ noteId: note.id });
+			const exist = await this.promoNotesRepository.exist({ where: { noteId: note.id } });
 
-			if (exist != null) {
+			if (exist) {
 				throw new ApiError(meta.errors.alreadyPromoted);
 			}