CI fails when it can't install ffmpeg, which happens frequently

Our CI installs ffmpeg using a 3rd party GH action which downloads custom package from a site, which fails from time to time.

Re-running the job usually helps.

Few ideas on how to solve that:
- Use Playwright's own ffmpeg (this might be enough for our needs, but might require some binary discovery as it is not officially exposed by Playwright)
- Try to do more image cacheing which would hopefully reduce the downloads and failures (it was supposed to be handled by the GH action...)
- Find a more reliable place to get it

Start by locating the CI workflow step that installs ffmpeg and inspect the third-party GitHub Action and its download behavior. Evaluate the listed Playwright, image-caching, and alternate-source options; done means CI can obtain ffmpeg reliably and the affected jobs pass without repeated reruns.

Written by the indexing model from the issue text.