fix: improve "yq" arguments in justfile

No more pipe redirection. We tell yq to read the file itself. And we use `--` to ensure it never interprets files as flags.

usr/share/ublue-os/just/justfile

@@ -26,7 +26,7 @@ distrobox-ubuntu:
 setup-flatpaks:
   #!/usr/bin/env bash
   echo 'Installing flatpaks from the ublue recipe ...'
-  flatpaks=$(yq '.flatpaks[]' < /usr/share/ublue-os/recipe.yml)
+  flatpaks=$(yq -- '.firstboot.flatpaks[]' "/usr/share/ublue-os/recipe.yml")
   for pkg in $flatpaks; do \
       echo "Installing: ${pkg}" && \
       flatpak install --user --noninteractive flathub $pkg; \