deps: bump Spanner to 6.23.3 (#137)
deps: bump Spanner to 6.23.3 (#137)

* deps: bump Spanner to 6.23.3

* deps: define Spanner version once
GoogleCloudPlatform/pgadapter,GoogleCloudPlatform/pgadapter,GoogleCloudPlatform/pgadapter,GoogleCloudPlatform/pgadapter,GoogleCloudPlatform/pgadapter,GoogleCloudPlatform/pgadapter,GoogleCloudPlatform/pgadapter