[5.4] Fix Queue Worker database connection issue

[laurencei]

This PR solves #19242 as confirmed in that issue.

It relates to two separate issues:

1. The DetectsLostConnections trait should include some string around transaction issues on null (which would imply a lost connection).

2. A transaction error on null results in a Throwable - not an Exception - so we need to have worker check for lost connections on Throwable as well.