Avoid APT breaking when installing postfix-pcre

If postfix-pcre is installed before postfix, Puppet may fail with:

    Error: Execution of '/usr/bin/apt-get -q -y -o DPkg::Options::=--force-confold install postfix-pcre' returned 100: Reading package lists...
    Building dependency tree...
    Reading state information...
    Some packages could not be installed. This may mean that you have
    requested an impossible situation or if you are using the unstable
    distribution that some required packages have not yet been created
    or been moved out of Incoming.
    The following information may help to resolve the situation:
    The following packages have unmet dependencies:
     postfix-pcre : Depends: postfix (= 3.4.14-0+deb10u1) but it is not going to be installed
    E: Unable to correct problems, you have held broken packages.