fix: use information_schema instead of pg_catalog for dialect detection (#1708)

Author: olavloite

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPool.java

@@ -1764,7 +1764,7 @@ private enum Position {
       Statement.newBuilder(
               "SELECT 'POSTGRESQL' AS DIALECT\n"
                   + "FROM INFORMATION_SCHEMA.SCHEMATA\n"
-                  + "WHERE SCHEMA_NAME='pg_catalog'\n"
+                  + "WHERE SCHEMA_NAME='information_schema'\n"
                   + "UNION ALL\n"
                   + "SELECT 'GOOGLE_STANDARD_SQL' AS DIALECT\n"
                   + "FROM INFORMATION_SCHEMA.SCHEMATA\n"