Bug#983478: courier: Please revert the fam -> gamin change for bullseye

[Adrian Bunk <bunk@debian.org>]

Source: courier
Version: 1.0.15-1
Severity: serious

Incorrect information was given in #981513:
- gamin is expected to stay for a long time, while switching
  to inotify would still be preferred if it is an option
  (NFS does not support inotify) this is not urgent
- the release team has now decided that fam will stay in bullseye,
  it is expected that fam will be removed for bookworm

There are small incompatibilities between fam and gamin (see #510368).
Please switch courier back to fam for bullseye so that apt will not
install a different implementation depending on whether courier was
installed in bullseye or whether courier was upgraded from buster,
which would likely happen after the #981513 change.

Thanks, and sorry for the confusion.