[AIRFLOW-5089] Spanner compatibility bug causes missing imports (#5703)

setup.py

@@ -195,7 +195,7 @@ gcp = [
     'google-cloud-container>=0.1.1',
     'google-cloud-dlp>=0.11.0',
     'google-cloud-language>=1.1.1',
-    'google-cloud-spanner>=1.7.1',
+    'google-cloud-spanner>=1.7.1, <1.10.0',
     'google-cloud-storage~=1.16',
     'google-cloud-translate>=1.3.3',
     'google-cloud-videointelligence>=1.7.0',