build(deps): bump third-party/FFmpeg/FFmpeg from 9373b44 to 6400860 (#455)

Bumps [third-party/FFmpeg/FFmpeg](https://github.com/FFmpeg/FFmpeg) from `9373b44` to `6400860`.
- [Commits](FFmpeg/FFmpeg@9373b44...6400860)

---
updated-dependencies:
- dependency-name: third-party/FFmpeg/FFmpeg
  dependency-version: 6400860b9d4bec5ace91ec3a5e43ad76f9660579
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]