VLCMediaList and VLCTime: fix nullability annotations

This improves the nullability annotations for VLCTime and VLCMediaList.

changed milestone to %4.0

added Maintenance Minor labels

added 12 commits

• c9025569...a51b5435 - 10 commits from branch videolan:master
• 07cb3ba7 - VLCTime: fix nullability annotation
• d80d27e5 - VLCMediaList: fix nullability annotation

Compare with previous version

enabled an automatic merge when the pipeline for d80d27e5 succeeds

merged