Set LINUX_PORTABLE to off on CI

Sets LINUX_PORTABLE to off on CI. This matches what is default in
OBS Studio. Most developers won't know to change this, as the deb
file will install to the wrong place, causing the plugin not to load.

.github/scripts/.build.zsh

@@ -220,7 +220,7 @@ Usage: %B${functrace[1]%:*}%b <option> [<options>]
         ;;
       linux-*)
         if (( ${+CI} )) {
-          cmake_args+=(-DCMAKE_INSTALL_PREFIX=/usr)
+          cmake_args+=(-DCMAKE_INSTALL_PREFIX=/usr -DLINUX_PORTABLE=OFF)
         }
         num_procs=$(( $(nproc) + 1 ))
         ;;