update git trigger to match new workflow label on review-dev

review-dev has a new label called 'workflow' that combines approved and wip labels.
Updating the trigger for gate pipeline to match.

The gerrit workflow label is defined as:

[label "Workflow"]
        function = MaxWithBlock
        copyMinScore = false
	      copyAllScoresOnTrivialRebase = false
	      copyAllScoresIfNoCodeChange = false
        value = -1 Work in progress
        value =  0 Ready for reviews
        value = +1 Approved

Change-Id: Ieb7e2dde49cd64f2aa3dbf939c391492d73ed886