don't assume the user's shell knows about bashisms

For example, -n doesn't exist in zsh, and -p has a different
meaning. In general, I had to scroll through pages and pages of the
bash manpage to even figure out what does options do, so I prefer to
keep things simple and stay with a more classic "press enter to
continue".

I'm sure people can find the ENTER key if they were managing to find
the ANY key before. ;)

howto/upgrades/bullseye.md

@@ -126,8 +126,9 @@ See the "conflicts resolution" section below for how to handle
 
         apt-get update --allow-releaseinfo-change &&
         puppet agent --enable &&
-        puppet agent -t --noop &&
-        read -n1 -s -r -p "Press any key to continue, Ctrl-C to abort." &&
+        puppet agent -t --noop
+        printf "Press enter to continue, Ctrl-C to abort." &&
+        read -r _ &&
         (puppet agent -t || true) &&
         (puppet agent -t || true) &&
         rm -f /etc/apt/apt.conf.d/50unattended-upgrades.dpkg-dist /etc/bacula/bacula-fd.conf.ucf-dist /etc/ca-certificates.conf.dpkg-old /etc/cron.daily/bsdmainutils.dpkg-remove /etc/default/prometheus-apache-exporter.dpkg-dist /etc/default/prometheus-node-exporter.dpkg-dist /etc/ldap/ldap.conf.dpkg-dist /etc/logrotate.d/apache2.dpkg-dist /etc/nagios/nrpe.cfg.dpkg-dist /etc/ssh/ssh_config.dpkg-dist /etc/ssh/sshd_config.ucf-dist /etc/sudoers.dpkg-dist /etc/syslog-ng/syslog-ng.conf.dpkg-dist /etc/unbound/unbound.conf.dpkg-dist