Updates the Spanner client to 6.57.0 and modifies some test cases to
work with the newest version of the Spanner client. The manual changes
other than the dependency update are:
1. The Spanner client now supports PROTO and PROTO ENUM columns. This is
   also reflected in the RandomResultSetGenerator, which means that the
   number of columns is increased from 18 to 22.
2. The above addition of PROTO and PROTO ENUM means that the error
   message changes when you try to get a blob with a wrong column.
3. The newly introduced statement cache must be disabled, as there is a
   small bug that prevents the first query to include any default query
   options (e.g. optimizer version).