Spanner: pick up changes to GAPIC method configuration.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > You are running the synthesis script directly, this will be disabled in a future release of Synthtool. Please use python3 -m synthtool instead.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:2f6b261ee7fe1aedf238991c93a20b3820de37a343d0cacf3e3e9555c2aaf2ea
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/spanner/artman_spanner.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-v1.
synthtool > Replaced '# limitations under the License.\n\nimport google.api_core.grpc_helpers\n' in google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py.
synthtool > Replaced 'from google.cloud.spanner_v1.proto import spanner_pb2_grpc\n' in google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py.
synthtool > Replaced '(\\s+)return google.api_core.grpc_helpers.create_channel\\(\n' in google/cloud/spanner_v1/gapic/transports/spanner_grpc_transport.py.
synthtool > Replaced 'from google.cloud import spanner_v1' in tests/unit/gapic/v1/test_spanner_client_v1.py.
synthtool > Running generator for google/spanner/admin/instance/artman_spanner_admin_instance.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-instance-v1.
synthtool > Replaced "'google-cloud-spanner-admin-instance'" in google/cloud/spanner_admin_instance_v1/gapic/instance_admin_client.py.
synthtool > Replaced 'from google\\.cloud\\.spanner\\.admin\\.instance_v1.proto' in google/cloud/spanner_admin_instance_v1/proto/spanner_instance_admin_pb2_grpc.py.
synthtool > Replaced '====*' in google/cloud/spanner_v1/proto/transaction_pb2.py.
synthtool > Replaced '----*' in google/cloud/spanner_v1/proto/transaction_pb2.py.
synthtool > Replaced '~~~~*' in google/cloud/spanner_v1/proto/transaction_pb2.py.
synthtool > Running generator for google/spanner/admin/database/artman_spanner_admin_database.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/spanner-admin-database-v1.
synthtool > Replaced "'google-cloud-spanner-admin-database'" in google/cloud/spanner_admin_database_v1/gapic/database_admin_client.py.
synthtool > Replaced 'from google\\.cloud\\.spanner\\.admin\\.database_v1.proto' in google/cloud/spanner_admin_database_v1/proto/spanner_database_admin_pb2_grpc.py.
synthtool > Cleaned up 0 temporary directories.