Update change-hostname to use hostnamectl (#1803)

Resolves #1679

This change updates the `change-hostname` script to use `hostnamectl`
instead of editing `/etc/hostname` directly.

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debian-pkg/opt/tinypilot-privileged/scripts/change-hostname

@@ -68,7 +68,8 @@ printf "%s\n127.0.1.1 %s\n%s\n%s\n" \
   "${MARKER_START}" "${NEW_HOSTNAME}" "${MARKER_END}" "${OLD_ETC_HOSTS}" \
   > /etc/hosts
 
-# Populate new hostname to `/etc/hostname`.
-# Note that the value must be newline-terminated, see:
-# https://manpages.debian.org/stretch/systemd/hostname.5.en.html
-printf "%s\n" "${NEW_HOSTNAME}" > /etc/hostname
+# We use `hostnamectl set-hostname xyz` instead of `hostnamectl hostname xyz`
+# because `set-hostname` is backwards compatible with the Bullseye version of
+# `hostnamectl`. `hostnamectl hostname xyz` is only supported on the Bookworm
+# version.
+hostnamectl set-hostname "${NEW_HOSTNAME}"