Fix remaining mypy errors from full lib+test type check

- annotate the headers dict in DatasetsService.display
- declare container_name on the tee-stream integration test class

lib/galaxy/webapps/galaxy/services/datasets.py

@@ -690,7 +690,7 @@ class DatasetsService(ServiceBase, UsesVisualizationMixin):
         some point in the future without warning. Generally, data should be processed by its
         datatype prior to display (the default if raw is unspecified or explicitly false.
         """
-        headers = {}
+        headers: dict[str, str] = {}
         rval: Any = ""
         try:
             dataset_manager = self.dataset_manager_by_type[hda_ldda]

test/integration/objectstore/test_direct_download_redirect.py

@@ -37,6 +37,7 @@ BOTO3_DIRECT_DOWNLOAD_CONFIG = string.Template("""
 
 @integration_util.skip_unless_docker()
 class TestDirectDownloadRedirectIntegration(BaseObjectStoreIntegrationTestCase):
+    container_name: str
     object_store_cache_path: str
 
     @classmethod