[tests] Update user agent

[TobiGr]

• [x] I carefully read the contribution guidelines and agree to them.
• [x] I have tested the API against NewPipe.
• [x] I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

This updates the user agent used for testing purposes to a modern version.

This also modifies the RecordingDownloader to automatically prevent hitting rate limits ("sign in to confirm you are not a bot") + RecaptchaExceptions and handle them if they occur: There is now a max number of requests which are made per minute (default is 30). Requests are postponed if the limit is reached. When running into a RecaptchaException the RecordingDownloader waits between 35 and 60 seconds before retrying the request once again. This slows down the time for generating new mocks to ~5 minutes but prevents faulty mocks.

[!Warning] All YouTube tests passing the real tests also pass the new mock tests. However, the Bandcamp tests are failing locally now. Bandcamp tests run by GH Actions pass however.

[TobiGr]

All tests passing the real tests also pass the new mock tests.