Fix false positive and intempestive 'pending kernel update' messages …

…on EndeavourOS with systemd-boot

EndeavourOS does not use '/boot' to store 'vmlinuz*' files when using systemd-boot (I couldn't find much details about a specific reason for that, attemps at analyses [here](#74 (comment)).

This commit aims to make the script fallback to '/usr/lib/modules/*/vmlinuz*' if 'vmlinuz*' files are not found under '/boot'.
This prevents false positive and intempestive 'pending kernel update' messages on EndeavourOS + systemd-boot

src/script/arch-update.sh

@@ -372,7 +372,11 @@ pacnew_files() {
 
 # Definition of the kernel_reboot function: Verify if there's a kernel update waiting for a reboot to be applied
 kernel_reboot() {
-	kernel_compare=$(file /boot/vmlinuz* | sed 's/^.*version\ //' | awk '{print $1}' | grep "$(uname -r)")
+	if [ -f /boot/vmlinuz* ]; then
+		kernel_compare=$(file /boot/vmlinuz* | sed 's/^.*version\ //' | awk '{print $1}' | grep "$(uname -r)")
+	else
+		kernel_compare=$(file /usr/lib/modules/*/vmlinuz* | sed 's/^.*version\ //' | awk '{print $1}' | grep "$(uname -r)")
+	fi
 
 	if [ -z "${kernel_compare}" ]; then
 		echo -e "--Reboot required--\nThere's a pending kernel update on your system requiring a reboot to be applied\n"