completion: Invoke the command being completed

As suggested by Ville Skyttä in
https://gitlab.gnome.org/GNOME/glib/-/merge_requests/4012#note_2084405,
make sure to invoke the copy of the command which is being completed
when asking for completions of a given subcommand.

This avoids accidentally invoking any old `gdbus`/`gresource`/etc.
binary which is hanging around in another part of `$PATH`.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

gio/completion/gdbus

@@ -8,12 +8,15 @@
 
 
 __gdbus() {
+    local gdbus_binary
+    gdbus_binary="$1"
+
     local IFS=$'\n'
     local cur
     cur="$(_get_cword :)"
 
     local suggestions
-    suggestions="$(gdbus complete "${COMP_LINE}" "${COMP_POINT}")"
+    suggestions="$("$gdbus_binary" complete "${COMP_LINE}" "${COMP_POINT}")"
     # shellcheck disable=SC2207
     COMPREPLY=($(compgen -W "$suggestions" -- "$cur"))