fix: Use starred tuple unpacking on GCS artifact blob names

Merges https://github.com/google/adk-python/pull/1471

Fixes google#1436

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/1471 from bck-ob-gh:main 4c4f2b66ab1e6fde8b1a9d2b914dcb24040db144
PiperOrigin-RevId: 774809270

src/google/adk/artifacts/gcs_artifact_service.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 """An artifact service implementation using Google Cloud Storage (GCS)."""
+from __future__ import annotations
 
 import logging
 from typing import Optional
@@ -151,7 +152,7 @@ class GcsArtifactService(BaseArtifactService):
         self.bucket, prefix=session_prefix
     )
     for blob in session_blobs:
-      _, _, _, filename, _ = blob.name.split("/")
+      *_, filename, _ = blob.name.split("/")
       filenames.add(filename)
 
     user_namespace_prefix = f"{app_name}/{user_id}/user/"
@@ -159,7 +160,7 @@ class GcsArtifactService(BaseArtifactService):
         self.bucket, prefix=user_namespace_prefix
     )
     for blob in user_namespace_blobs:
-      _, _, _, filename, _ = blob.name.split("/")
+      *_, filename, _ = blob.name.split("/")
       filenames.add(filename)
 
     return sorted(list(filenames))