Test fixes for Kafka (#834)

Test fixes for Kafka:
- Consumer: isinstance(max_concurrency, int) instead of is not None:
  MagicMock won't pass the check
- Kafka test: updated expected topic name to
  tg.request.prompt.default (colons replaced with dots)

tests/unit/test_pubsub/test_kafka_backend.py

@@ -57,9 +57,9 @@ class TestKafkaParseTopic:
             backend._parse_topic('unknown:tg:topic')
 
     def test_topic_with_flow_suffix(self, backend):
-        """Topic names with flow suffix (e.g. :default) are preserved."""
+        """Topic names with flow suffix (e.g. :default) have colons replaced with dots."""
         name, cls, durable = backend._parse_topic('request:tg:prompt:default')
-        assert name == 'tg.request.prompt:default'
+        assert name == 'tg.request.prompt.default'
 
 
 class TestKafkaRetention:

trustgraph-base/trustgraph/base/consumer.py

@@ -58,7 +58,7 @@ class Consumer:
         # consumers in the same group causes rebalance storms where
         # no consumer can fetch. Cap to the backend's limit.
         max_concurrency = getattr(backend, 'max_consumer_concurrency', None)
-        if max_concurrency is not None and concurrency > max_concurrency:
+        if isinstance(max_concurrency, int) and concurrency > max_concurrency:
             logger.info(
                 f"Capping concurrency from {concurrency} to "
                 f"{max_concurrency} (backend limit)"