functions: cloud-init clean script needs to declar interpreter

LP: #2055729

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (24.04.45) UNRELEASED; urgency=medium
+
+  [ Chad Smith ]
+  * Fix cloud-init clean script, by declaring the interpreter
+
+ -- Dan Bungert <daniel.bungert@canonical.com>  Fri, 01 Mar 2024 15:21:21 -0700
+
 livecd-rootfs (24.04.44) noble; urgency=medium
 
   * Switch to using the candidate channel for the ubuntu-image snap. This way

live-build/functions

@@ -1099,6 +1099,7 @@ EOF
         # Allow cloud-init clean to inform of strict network-manager config
         mkdir -p chroot/etc/cloud/clean.d
         cat <<EOF > chroot/etc/cloud/clean.d/99-installer-use-networkmanager
+#!/bin/sh
 # Inform clone image creators about strict network-manager cfg for cloud-init
 if [ -f /etc/cloud/cloud.cfg.d/99-installer-use-networkmanager.cfg ]; then
   echo "WARNING: cloud-init network config is limited to using network-manager."