flaky kokoro required tests blocking PRs

- https://btx.cloud.google.com/invocations/34499825-1183-4aed-8036-669e4ab85ff4/targets/cloud-devrel%2Fclient-libraries%2Fjava%2Fgoogle-cloud-java%2Fpresubmit%2Fdatastore-integration/details
- https://btx.cloud.google.com/invocations/40bedb3d-7df1-4c39-9b2b-027d93673bef/targets/cloud-devrel%2Fclient-libraries%2Fjava%2Fgoogle-cloud-java%2Fpresubmit%2Flogging-integration/details
- https://btx.cloud.google.com/invocations/81fd67b2-2c52-4fb9-bc94-1e60ffb409b3/targets/cloud-devrel%2Fclient-libraries%2Fjava%2Fgoogle-cloud-java%2Fpresubmit%2Fspanner-integration/details

Start with the three linked Kokoro invocation details for the datastore, logging, and spanner integration presubmit targets. Compare the reported failures and the corresponding integration-test runs to determine whether the tests are flaky. Done means the required presubmit tests no longer block healthy pull requests, with the relevant failure evidence and verification recorded.

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