cerbero: Backport fix for removed loop param of PriorityQueue()
Backport to 1.18 of: !756 (merged)
1.18 needs to maintain support for Python 3.6, so we need to add the argument conditionally.
Backport to 1.18 of: !756 (merged)
1.18 needs to maintain support for Python 3.6, so we need to add the argument conditionally.