chore: Bump minimum required version of spanner-graph-notebook to 1.1.5

This fixes an issue where forcegraph is unavailable for external server.

Author: ericfe-google

setup.py

@@ -57,7 +57,7 @@
     "bigframes": ["bigframes >= 1.17.0"],
     "geopandas": ["geopandas >= 1.0.1"],
     "spanner-graph-notebook": [
-        "spanner-graph-notebook >= 1.1.3",
+        "spanner-graph-notebook >= 1.1.5",
         "portpicker",
     ],
 }