narval #2133826 thread-safety issues with NarvalProcessManager._running_tasks [validation pending]

the set is accessed/modified from different threads with no locking.

prioritynormal
typebug
done in3.2.0
load0.500
load left0.000
closed by#24411374e65f [narvalbot] Protect operations on the running_tasks set with a lock (closes #2133826)