GST_PLUGIN_SYSTEM_PATH is not respecting multiarch
I fixed that over at the Fd.o side a while ago, and though we would inherit it, but we need to fix it here too.
currently GST_PLUGIN_SYSTEM_PATH
point to /usr/lib/gstreamer-1.0
which is invalid since everything in installed under the arch like on fd.o.
fdo MR: https://gitlab.com/freedesktop-sdk/freedesktop-sdk/merge_requests/527
➜ ~ flatpak run org.gnome.Sdk//3.30
sh-4.4$ echo $GST_PLUGIN_SYSTEM_PATH
/app/lib/gstreamer-1.0:/usr/lib/extensions/gstreamer-1.0:/usr/lib/gstreamer-1.0
sh-4.4$ exit
exit
➜ ~ flatpak run org.freedesktop.Sdk//18.08
sh-4.4$ echo $GST_PLUGIN_SYSTEM_PATH
/app/lib/gstreamer-1.0:/usr/lib/extensions/gstreamer-1.0:/usr/lib/x86_64-linux-gnu/gstreamer-1.0
sh-4.4$