pin out some package from Debian OpenStack Team repos

Debian OpenStack Team backports many packages to get their stuff done.
Sometimes something goes wrong:

INFO:kolla.common.utils.kolla-toolbox:The following packages have unmet dependencies:
INFO:kolla.common.utils.kolla-toolbox: git : Depends: git-man (< 1:2.30.2-.) but 1:2.34.1-1~bpo11+1 is to be installed
INFO:kolla.common.utils.kolla-toolbox:E: Unable to correct problems, you have held broken packages.

So let pin out problematic packages as we are fine with bullseye version
of git.

Change-Id: I8c740655c7f7803d9ab36dac79d30e35e65dd586
(cherry picked from commit 2553c18)

Author: hrw

docker/base/apt_preferences.debian

@@ -22,3 +22,8 @@ Pin-Priority: -1000
 Package: openvswitch* python3-openvswitch ovn-*
 Pin: release n=bullseye-backports
 Pin-Priority: 1024
+
+# NOTE(hrw): Debian OpenStack Team repo has some backports we do not want
+Package: git*
+Pin: release n=bullseye
+Pin-Priority: 1024