Bump SpotBugs in the stable CI template for %19.0

Description

As discussed in this comment, we were unable to bump SpotBugs to v6 in the stable CI template for the %18.0 milestone due to an unapproved breaking change (removal of JDK 11 support). As a result, the default SpotBugs job remains on v5 for all 18.x milestones.

This issue is to track the planned upgrade of SpotBugs to v6 (or v7) in the %19.0 milestone.