[Flaky test] TestGenerateProcessorList: `panic: Log in goroutine after TestGenerateProcessorList has completed`

## Flaky Test

* **Test Name:** TestGenerateProcessorList
* **Link:** https://github.com/elastic/beats/blob/0e87812a090a6e5634f2361ed153ebbb2f2b7b40/libbeat/publisher/processing/default_test.go#L43
* **Branch:** 8.19
* **Artifact Link:** https://buildkite.com/elastic/beats-libbeat/builds/22868/steps/canvas?sid=019a5537-1fc0-4bfb-8159-14fba7e6503d#019a554e-27e6-43d1-8d05-100be1d8dc14/193-592
* **Notes:** The root cause is also present on `main`, but the panic has been mitigated by using a no-op logger. See https://github.com/elastic/beats/issues/47527 for more details.

### Stack Trace

```
2025-11-05 13:54:43 EST
panic: Log in goroutine after TestGenerateProcessorList has completed: 2025-11-05T18:46:23.758Z DEBUG add_cloud_metadata add_cloud_metadata: received disposition for hetzner after 3.764475ms. result=[provider:hetzner, error=failed with http status code 404, metadata={}]
2025-11-05 13:54:43 EST
panic: Log in goroutine after TestGenerateProcessorList has completed: 2025-11-05T18:46:23.758Z DEBUG add_cloud_metadata add_cloud_metadata: fetchMetadata ran for 3.818102ms
2025-11-05 13:54:43 EST

```

Start with TestGenerateProcessorList at libbeat/publisher/processing/default_test.go:43 and review the linked Buildkite artifact for the failure. Read issue 47527 for the related mitigation and investigate why logging continues after the test completes. Done means the test no longer produces the post-completion logging panic.

Written by the indexing model from the issue text.