Tracing Tests E2E GLOBAL-OTEL GRPC: document reference get() failed

This test failed! To configure my behavior, see [the Flaky Bot documentation](https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot). If I'm commenting on this issue too often, add the `flakybot: quiet` label and I will stop commenting. --- commit: 4a075ebcb402b690671c885e716b78d73a25d2de buildURL: [Build Status](https://source.cloud.google.com/results/invocations/630c7651-1a9f-4c8a-af1c-91ff9dd2a5e5), [Sponge](http://sponge2/630c7651-1a9f-4c8a-af1c-91ff9dd2a5e5) status: failed