style: fix whitespace (black error)

Author: yt-ms

tests/unit/view/test_container_view.py

@@ -20,7 +20,7 @@
 def test_external_system_boundary_preserved():
     """
     Test the externalSoftwareSystemBoundariesVisible flag appears in the JSON.
-    
+
     Not having this set means that Structurizr assumes it is false (see
     https://github.com/Midnighter/structurizr-python/issues/67).  When exported
     from Structurizr, the flag is present whether true or false, so check that