chore: Improve logic for the 'NoNotification' option (#307)

Only check for 'notify-send' presence if the NoNotification option is not set

src/lib/check.sh

@@ -26,7 +26,7 @@ sed -ri 's/\x1B\[[0-9;]*m//g' "${statedir}/current_updates_check"
 if [ -n "${update_available}" ]; then
 	icon_updates-available
 
-	if [ -n "${notification_support}" ] && [ -z "${no_notification}" ]; then
+	if [ -n "${notification_support}" ]; then
 		if ! diff "${statedir}/current_updates_check" "${statedir}/last_updates_check" &> /dev/null; then
 			update_number=$(wc -l "${statedir}/current_updates_check" | awk '{print $1}')
 			# shellcheck disable=SC2154

src/lib/common.sh

@@ -133,8 +133,10 @@ fi
 flatpak_support=$(command -v flatpak)
 
 # Check if notify-send is installed for the optional desktop notification support
-# shellcheck disable=SC2034
-notification_support=$(command -v notify-send)
+if [ -z "${no_notification}" ]; then
+	# shellcheck disable=SC2034
+	notification_support=$(command -v notify-send)
+fi
 
 # Definition of the elevation command to use (depending on which one is installed on the system and if it's not already defined in arch-update.conf)
 if [ -z "${su_cmd}" ]; then