fix: Use starred tuple unpacking on GCS artifact blob names for versions function

Author: zshehov

src/google/adk/artifacts/gcs_artifact_service.py

@@ -191,6 +191,6 @@ async def list_versions(
     blobs = self.storage_client.list_blobs(self.bucket, prefix=prefix)
     versions = []
     for blob in blobs:
-      _, _, _, _, version = blob.name.split("/")
+      *_, version = blob.name.split("/")
       versions.append(int(version))
     return versions

tests/unittests/artifacts/test_artifact_service.py

@@ -253,7 +253,7 @@ async def test_list_versions(service_type):
   app_name = "app0"
   user_id = "user0"
   session_id = "123"
-  filename = "filename"
+  filename = "with/slash/filename"
   versions = [
       types.Part.from_bytes(
           data=i.to_bytes(2, byteorder="big"), mime_type="text/plain"