Fix tests for MG property graph

[eriknw]

Small PR to fix MGPG tests.

Note that @galipremsagar fixed the equivalent tests for test_property_graph.py in #3036 by using s._constructor, which is pretty slick.

Also, start_dask_client returns a tuple of client and cluster now, so I updated the dask_client fixture so the cluster can be closed properly.

[codecov-commenter]

Codecov Report

Base: 57.60% // Head: 57.60% // No change to project coverage 👍

Coverage data is based on head (957829c) compared to base (324f370).
Patch has no changes to coverable lines.

Additional details and impacted files

@@              Coverage Diff              @@
##           branch-23.02    #3090   +/-   ##
=============================================
  Coverage         57.60%   57.60%           
=============================================
  Files               147      147           
  Lines              9227     9227           
=============================================
  Hits               5315     5315           
  Misses             3912     3912           

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[alexbarghi-nv]

👍

[BradReesWork]

/merge