Bug 1660506 - [taskgraph] Don't overwrite 'backstop' parameter if set from try_task_config.json, r=taskgraph-reviewers,aki

I found myself needing to test a push with 'backstop=True' on try. Though, I
couldn't set it because the call to 'is_backstop' happens after the
'try_task_config' parameters are added in. This adds a simple check to handle
that case.

Differential Revision: https://phabricator.services.mozilla.com/D88910

taskcluster/taskgraph/util/backstop.py

@@ -27,6 +27,10 @@ def is_backstop(
     Returns:
         bool: True if this is a backtop, otherwise False.
     """
+    # In case this is being faked on try.
+    if params.get('backstop', False):
+        return True
+
     project = params["project"]
     pushid = int(params["pushlog_id"])
     pushdate = int(params["pushdate"])