[__jitsi_meet]: Fix deprecated usage of __debconf_set_selections.

Replace the --file parameter with the --line parameter, as recommended
since cdist 6.9.6.

type/__jitsi_meet/manifest

@@ -51,9 +51,7 @@ export require="${require} __apt_source/jitsi_meet __apt_update_index"
 # Pre-feed debconf settings, so Jitsi's installation has a good config
 # shellcheck source=type/__jitsi_meet/files/debconf_settings.sh
 . "${__type}/files/debconf_settings.sh"  # This defines DEBCONF_SETTINGS
-__debconf_set_selections jitsi_meet --file - <<EOF
-${DEBCONF_SETTINGS}
-EOF
+__debconf_set_selections jitsi_meet --line "${DEBCONF_SETTINGS}"
 export require="${require} __debconf_set_selections/jitsi_meet"
 
 # Install and upgrade packages as needed