fix(test): add importorskip guard for S3 optional dependencies

The S3 artifact tests require aioboto3 and botocore which are only
installed with the [s3] extra. CI runs with --extra test only, so
these tests fail with ModuleNotFoundError on collection.

Adding pytest.importorskip() at module level gracefully skips the
entire test file when the S3 dependencies aren't available.

Author: miyannishar

tests/unittests/artifacts/test_s3_artifact_service.py

@@ -28,6 +28,8 @@
 from google.genai import types
 import pytest
 
+pytest.importorskip("aioboto3")
+pytest.importorskip("botocore")
 
 
 FIXED_DATETIME = datetime(2025, 1, 1, 12, 0, 0, tzinfo=timezone.utc)