Release 1.51.0 has dependency version conflicts

[olavloite]

Adding a dependency on google-cloud-spanner version 1.51.0 to a project will cause the following build error:

Could not resolve dependencies for project com.google.cloud:spanner-example-runner:jar:0.0.1-SNAPSHOT: Failed to collect dependencies for com.google.cloud:spanner-example-runner:jar:0.0.1-SNAPSHOT: Could not resolve version conflict among [com.google.cloud:google-cloud-spanner:jar:1.51.0 -> io.grpc:grpc-api:jar:1.28.0, com.google.cloud:google-cloud-spanner:jar:1.51.0 -> io.grpc:grpc-auth:jar:1.28.0 -> io.grpc:grpc-api:jar:[1.28.0,1.28.0], com.google.cloud:google-cloud-spanner:jar:1.51.0 -> io.grpc:grpc-protobuf:jar:1.28.0 -> io.grpc:grpc-api:jar:1.28.0, com.google.cloud:google-cloud-spanner:jar:1.51.0 -> io.grpc:grpc-protobuf:jar:1.28.0 -> io.grpc:grpc-protobuf-lite:jar:1.28.0 -> io.grpc:grpc-api:jar:1.28.0, com.google.cloud:google-cloud-spanner:jar:1.51.0 -> io.grpc:grpc-stub:jar:1.28.0 -> io.grpc:grpc-api:jar:1.28.0, com.google.cloud:google-cloud-spanner:jar:1.51.0 -> com.google.cloud:google-cloud-core-grpc:jar:1.93.2 -> io.grpc:grpc-api:jar:1.27.2, com.google.cloud:google-cloud-spanner:jar:1.51.0 -> com.google.cloud:google-cloud-core-grpc:jar:1.93.2 -> io.grpc:grpc-core:jar:1.27.2 -> io.grpc:grpc-api:jar:[1.27.2,1.27.2]]