Login __generated__ file with mutation defined in lowercase is causing errors

Following the official documentation and the rest of the tutorial, queries and mutations are defined with the first letter in uppercase (PascalCase). However, in this [part of the tutorial](https://www.apollographql.com/docs/tutorial/mutations/#define-the-mutation) the mutation `Login` is defined lowercase (I see that in the final version of the tutorial this is corrected):

```gql
export const LOGIN_USER = gql`
mutation login($email: String!) {
login(email: $email)
}
`;
```

The corresponding generated file (`pages/__generated__/login.ts`), `Login` type appears as well in lowercase but the related code is assuming they are in uppercase, throwing errors:

```gql
const [login, { loading, error }] = useMutation<
LoginTypes.Login,
LoginTypes.LoginVariables
>(LOGIN_USER);
```

The mutation `Login` in the integration tests (`server/src/__tests__/integration.js`) is also defined in lowercase:
```gql
const LOGIN = gql`
mutation login($email: String!) {
login(email: $email)
}
`;
```

检查 issue 中链接的 mutation 部分、生成的 pages/__generated__/login.ts 文件以及 server/src/__tests__/integration.js。确认 mutation 命名和生成类型引用始终使用相同的大小写；教程代码和集成测试应保持一致，并且不再产生报告中的错误。

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