message: fix: clean up mail e2e
diff: import fs from 'fs';
  import { join, resolve } from 'path';
  +import * as fsExtra from 'fs-extra';
  import { MailConfig, MailResponse, sendMail } from '@sap-cloud-sdk/mail-client';
  describe('Mail', () => {
  + beforeEach(async () => {
  + fsExtra.emptyDirSync(join(resolve('test'), 'mail', 'test-output'));
  + });
  +
  const defaultMailOptions: MailConfig = {
  from: '"FROM" <from@example.com>',
  to: 'TO1@example.com, TO2@example.com',
  