[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

从 issue 中显示的 iam_samples 失败开始，并检查 QueryTestablePermissions 入口点。重现 Fedora 36 UBSAN Cloud Build，或将其与原始日志进行比较，以确定不可用的 IAM 服务是否是暂时性的。完成的标准是识别出一个可采取行动的测试失败和具体修复，或者确认当前不需要修改代码。

由索引模型根据 Issue 内容生成。