I am trying to connect to my postgres docker container using DBeaver and I am receiving the following error. FATAL: password authentication failed for user "redmine"

I have in the past, and it was accurate. The postgresql service wasn't running. The error may also arise if a firewall is preventing the connection. But given that you are connecting from localhost (or at least appear to be), a firewall issue seems unlikely.
(it can happen if you are connecting using the wrong port, too, of course)