ReCaptcha webview continues playing in background

[Douile]

Checklist

• I am using the latest version - fd4e1b8 (development build) >= v0.21.7
• I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• This issue contains only one bug. I will open one issue for every bug report I want to file.

Steps to reproduce the bug

1. Play video while blocked by captcha
2. Open captcha webview (press solve)
3. Solve captcha and answer GDPR questions
4. Wait for ad to start playing
5. Press done (tick in top-right)

Actual behavior

After the webview closes the ad continues playing in the background

Expected behavior

The webview stops playing any videos loaded. Probably best if it navigates to an empty (about:blank) page so the youtube website's javascript isn't sending requests in the background.

Device info

• Android version/Custom ROM version: 11
• Device model: N/A