Bug 1844298 - gecko_taskgraph: assert payload/index builders names are unique r=taskgraph-reviewers,gabriel DONTBUILD

The task transform module keeps registries of payload and index
builders, identified by a "name" string; AFAICT nothing prevents
registering different functions under the same name, which seems
potentially confusing.

Differential Revision: https://phabricator.services.mozilla.com/D183960

taskcluster/gecko_taskgraph/transforms/task.py

@@ -291,6 +291,7 @@ def payload_builder(name, schema):
     )
 
     def wrap(func):
+        assert name not in payload_builders, f"duplicate payload builder name {name}"
         payload_builders[name] = PayloadBuilder(schema, func)
         return func
 
@@ -303,6 +304,7 @@ index_builders = {}
 
 def index_builder(name):
     def wrap(func):
+        assert name not in index_builders, f"duplicate index builder name {name}"
         index_builders[name] = func
         return func