fix: resolve with non-lowercased acct is broken (#15813)

* fix: resolve with non-lowercased acct is broken

* docs(changelog): Fix: 大文字を含むユーザの URL で紹介された場合に 404 エラーを返す問題

packages/backend/test/unit/entities/UserEntityService.ts

@@ -74,7 +74,7 @@ describe('UserEntityService', () => {
 					...userData,
 					id: genAidx(Date.now()),
 					username: un,
-					usernameLower: un,
+					usernameLower: un.toLowerCase(),
 				})
 				.then(x => usersRepository.findOneByOrFail(x.identifiers[0]));