chore: Add pandas to the pip requirements for the ray data system test

PiperOrigin-RevId: 689500768

Author: yinghsienwu

tests/system/vertex_ray/test_ray_data.py

@@ -125,7 +125,10 @@ def test_ray_data(self, cluster_ray_version):
                 # Path to the local directory that contains the my_script.py file
                 runtime_env={
                     "working_dir": temp_dir,
-                    "pip": ["google-cloud-aiplatform[ray]==" + SDK_VERSION],
+                    "pip": [
+                        "pandas==2.1.4",
+                        "google-cloud-aiplatform[ray]==" + SDK_VERSION,
+                    ],
                 },
             )