need a plan to keep pgbackrest at a stable version across the fleet

We've had an issue today with pgbackrest on gitlab-02: it got upgraded to version 2.56.0 which just became available on the pgdg (upstream postgresql) apt archive so the backup stopped working since all other hosts are using version 2.55.1

Most of our hosts where pgbackrest is used have 2.55.1 installed from the debian trixie archive, but now pgdg is out of sync with that.

we were able to find a mirror of the pgdg archive that still contained the debian 12.0-specific 2.55.1 .deb that used to be present on pgdg (it's not anymore) and after verifying the .deb's contents and signatures we were able to downgrade pgbackrest on gitlab-02. now the package is marked as held on both of the bookworm hosts using pgbackrest.

We won't be able to upgrade the two bookworm hosts left (gitlab-02 and puppetdb-01) for a little while, so we need to come up with a plan to stick to a more stable version that's available across all of the server fleet.

Some possibilities of how we could achieve that:

1. as soon as debian trixie's release happens (planned to be on august 9th) request or send ourselves the version of the package from trixie to bookworm-backports. then add a pin to force that package to come from the debian archive (so block upgrades from pgdg for that specific package)
2. install the pgdg source everywhere we use pgbackrest and always track the version from there.
   • if we do that, we'll have to watch out for unexpected upgrades of postgresql on all trixie hosts.