Fix NoMethodError for ProcessCommitWorker

What does this MR do and why?

Contributes to #557695 (closed)

Problem

WorkItem object doesn't implement group method. Without it system notes failed to generate and raise an error in ProcessCommitWorker.

Solution

WorkItem defines namespace with a pointer to a group. It could be used to identify the group.

References

NoMethodError: ProcessCommitWorker undefined me... (#557695 - closed)

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Related to #557695 (closed)