[Flake] iam_samples: service is currently unavailable

```
2022-08-23T14:52:42.871774000Z [DEBUG] <140010620792512> QueryTestablePermissions() << google.iam.admin.v1.QueryTestablePermissionsRequest {
full_resource_name: "//iam.googleapis.com/projects/cloud-cpp-testing-resources/serviceAccounts/iam-test-sa@cloud-cpp-testing-resources.iam.gserviceaccount.com"
} (./google/cloud/internal/log_wrapper.h:91)
2022-08-23T14:52:47.887830000Z [DEBUG] <140010620792512> QueryTestablePermissions() >> status=UNAVAILABLE: The service is currently unavailable. (./google/cloud/internal/log_wrapper.h:94)
libc++abi: terminating with uncaught exception of type std::runtime_error: Error in non-idempotent operation QueryTestablePermissions: The service is currently unavailable.
```

* GCB: https://console.cloud.google.com/cloud-build/builds;region=us-east1/5675238e-b71b-4114-9cd3-b8d6fdaeb029;tab=detail?project=cloud-cpp-testing-resources
* Raw: https://storage.googleapis.com/cloud-cpp-community-publiclogs/logs/google-cloud-cpp/main/a4356c26e063a059372e43c3d3f0792d3be9070c/fedora-36-ubsan/log-5675238e-b71b-4114-9cd3-b8d6fdaeb029.txt

Start with the iam_samples failure shown in the issue and inspect the QueryTestablePermissions entry point. Reproduce or compare the Fedora 36 UBSAN Cloud Build and raw log to determine whether the unavailable IAM service is transient. Done means identifying an actionable test failure and a specific fix or confirming that no code change is currently warranted.

Written by the indexing model from the issue text.