Bug 1643689 - Backed out changeset 10110918b6c0

This was causing |mach try auto| to stop selecting manifests.

Differential Revision: https://phabricator.services.mozilla.com/D90553

taskcluster/taskgraph/optimize/__init__.py

@@ -491,10 +491,10 @@ def split_bugbug_arg(arg, substrategies):
 
     Many bugbug based optimizations require passing an empty dict by reference
     to communicate to downstream strategies. This function passes the provided
-    arg to the first strategies and a shared empty dict to last two (bugbug
-    based) strategies.
+    arg to the first strategies and an empty dict to last (bugbug based)
+    strategy.
     """
-    return [arg] * (len(substrategies) - 2) + [{}] * 2
+    return [arg] * (len(substrategies) - 1) + [{}]
 
 
 # Trigger registration in sibling modules.

taskcluster/test/test_mach_try_auto.py

@@ -69,6 +69,7 @@ def test_only_important_manifests(params, full_task_graph, filter_tasks):
         pytest.param(
             lambda t: t.kind == "build-signing",
             id="no build-signing",
+            marks=pytest.mark.xfail,
         ),
         pytest.param(
             lambda t: t.kind == "upload-symbols",