Flaky spanner test `client::tests::transaction_timeout_respected` timeouts on `run`

[haphungw]

Error Log:

failures:
---- client::tests::transaction_timeout_respected stdout ----
thread 'client::tests::transaction_timeout_respected' (81097) panicked at src/spanner/src/client.rs:2020:16:
Transaction should have succeeded: Error { kind: Timeout, source: Some(Status { code: Cancelled, message: "Timeout expired", source: Some(tonic::transport::Error(Transport, TimeoutExpired(()))) }) }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
    client::tests::transaction_timeout_respected
test result: FAILED. 1341 passed; 1 failed; 1 ignored; 0 measured; 0 filtered out; finished in 6.39s
error: test failed, to rerun pass `-p google-cloud-spanner --lib`

https://pantheon.corp.google.com/cloud-build/builds;region=us-central1/3d85359f-681e-4216-bfdf-e0d014c9d4e3?project=rust-sdk-testing&pli=1&e=SqlStudioMysqlLaunch::SqlStudioMysqlEnabled&mods=allow_workbench_image_override