[Backport release-25.11] flowblade: set GDK_BACKEND=x11 and SDL_VIDEODRIVER=x11 as it doesn't support wayland (#465839)

pkgs/by-name/fl/flowblade/package.nix

@@ -57,6 +57,8 @@ stdenv.mkDerivation rec {
     makeWrapper $out/flowblade/flowblade $out/bin/flowblade \
       --set FREI0R_PATH ${frei0r}/lib/frei0r-1 \
       --set LADSPA_PATH ${ladspaPlugins}/lib/ladspa \
+      --set GDK_BACKEND x11 \
+      --set SDL_VIDEODRIVER x11 \
       --prefix PATH : "${lib.makeBinPath [ ffmpeg ]}" \
       ''${gappsWrapperArgs[@]}