kernel-install/90-loaderentry: do not add multiple systemd.machine_id options

Do not unconditionally add a new systemd.machine_id command line option, first
check if it already exists with the expected value.

Fixes #25203

src/kernel-install/90-loaderentry.install

@@ -85,7 +85,7 @@ BOOT_OPTIONS="${BOOT_OPTIONS% }"
 # command line with the machine ID we use, so that the machine ID remains
 # stable, even during factory reset, in the initrd (where the system's machine
 # ID is not directly accessible yet), and if the root file system is volatile.
-if [ "$ENTRY_TOKEN" = "$MACHINE_ID" ]; then
+if [ "$ENTRY_TOKEN" = "$MACHINE_ID" ] && ! echo "$BOOT_OPTIONS" | grep -q "systemd.machine_id=$MACHINE_ID"; then
     BOOT_OPTIONS="$BOOT_OPTIONS systemd.machine_id=$MACHINE_ID"
 fi