multimedia/gstreamer1-plugins-svt-av1: update to 2.1.2

Changes: https://gitlab.com/AOMediaCodec/SVT-AV1/-/releases/v2.1.0
Changes: https://gitlab.com/AOMediaCodec/SVT-AV1/-/releases/v2.1.1
Changes: https://gitlab.com/AOMediaCodec/SVT-AV1/-/releases/v2.1.2
Reported by: Repology, /r/AV1