Bump FedericoCarboni/setup-ffmpeg from 2 to 3 in /.github/workflows

Bumps [FedericoCarboni/setup-ffmpeg](https://github.com/federicocarboni/setup-ffmpeg) from 2 to 3.
- [Release notes](https://github.com/federicocarboni/setup-ffmpeg/releases)
- [Commits](https://github.com/federicocarboni/setup-ffmpeg/compare/v2...v3)

---
updated-dependencies:
- dependency-name: FedericoCarboni/setup-ffmpeg
  dependency-version: '3'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/mocha.yml

@@ -30,7 +30,7 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-node-v${{ matrix.node }}-
           working-directory: ./backend
-      - uses: FedericoCarboni/setup-ffmpeg@v2
+      - uses: FedericoCarboni/setup-ffmpeg@v3
         id: setup-ffmpeg
       - name: Install Dependencies
         run: npm install