chore(deps): Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/build-ffmpeg.yaml

@@ -122,7 +122,7 @@ jobs:
 
     steps:
       - name: Download FFmpeg binaries
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: ffmpeg-${{ matrix.os }}
 
@@ -160,7 +160,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download FFmpeg archives
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           pattern: ffmpeg-archive-*
           merge-multiple: true