php-horde is re-uploaded and breaks in autopkgtests

Due to
https://bugs.launchpad.net/ubuntu/+source/php-horde/+bug/1868281
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=942282

php-horde-* was removed from Focal and Debian.

It is re-adopted now and re-uploaded.
That triggers a lot of test fails (broken dependencies) in groovy-proposed.

Right now we can't do too much, if we remove it we just have to re-sync later.
Steps:
 1. keep things in proposed, but mark them with a bug as update-excuse (this bug)
 2. wait until php-horde passed the new queue and is in groovy-proposed
 3. reschedule the tests with the right dependencies to horde and horde-test

Example:
  $ wget https://people.canonical.com/~ubuntu-archive/proposed-migration/update_excuses.html
  $ for p in $(grep -Hrn '>php-horde-.*</a> (- to <a href=' update_excuses.html | sed -e 's/.*>php-horde-/php-horde-/' | sed -e 's/<\/a>.*//' ); do retry-autopkgtest-regressions --series groovy --blocks "${p}"; done | sed -e 's/$/&trigger=php-horde-test%2F2.6.3%2Bdebian0-5&trigger=php-horde%2F5.2.21%2Bdebian1-1/'

Setting to incomplete initially as we wait on php-horde this isn't actionable right now