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)
}
`;
```

Esamina la sezione sulla mutation collegata nell'issue, il file generato pages/__generated__/login.ts e server/src/__tests__/integration.js. Verifica che il nome della mutation e i riferimenti ai tipi generati usino la stessa combinazione di maiuscole e minuscole ovunque; il codice del tutorial e il test di integrazione devono essere coerenti e non produrre più gli errori segnalati.

Scritto dal modello di indicizzazione a partire dal testo della issue.