vlc-debian-unstable: add gstreamer packages

This enables building the gstreamer decode plugin in CI.

It should catch issues like vlc#27980 (closed) beforehand.

Thinking about it some more, while this will enable compiling the gstreamer code, it won't catch the aforementioned bug since the image is uing GCC 12, and the bug only manifests itself with GCC 10 or lower (or clang).

resolved all threads

approved this merge request

added 19 commits

• bf5a45dc...f5a46723 - 18 commits from branch videolan:master
• 6e8cb6bf - vlc-debian-unstable: add gstreamer packages

Compare with previous version

merged

@JohannesKauffmann I'll let you do the update of the Gitlab file on VLC 4.0.

mentioned in issue #4 (closed)