[newbie-contributor] New contributor docs review — invalid Filebeat integration-test path

## Summary
The shared contributor testing guide gives a Filebeat integration-test command that fails immediately after the guide's own cd filebeat step. This blocks a new contributor from running the documented manual integration-test workflow.

## Findings

### 1. Filebeat integration-test example uses an invalid package path

**Where:** docs/extend/testing.md:35-46, under Running Go Integration Tests.

**Problem:** The example changes into the filebeat directory at line 38, then runs go test ./filebeat/... -tags integration at line 46. From that directory, the valid package pattern is ./...; ./filebeat/... resolves to a nonexistent filebeat/filebeat directory.

**Evidence:** In the current checkout, filebeat/ exists but filebeat/filebeat does not. Running the documented command from filebeat/ produces:

pattern ./filebeat/...: lstat ./filebeat/: no such file or directory
FAIL ./filebeat/... [setup failed]
FAIL

**Impact:** Contributors following the guide cannot execute the documented integration tests and must infer that the extra filebeat/ path should be removed.

**Suggested fix:** Change line 46 to go test ./... -tags integration, or document the command from the repository root as go test ./filebeat/... -tags integration. Add a lightweight validation for copyable contributor commands to prevent path drift.

## Suggested Actions

- [ ] Correct the Filebeat integration-test package path in docs/extend/testing.md.
- [ ] Validate the command from the directory shown immediately above it.

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> - [x] expires on Jul 28, 2026, 2:51 PM UTC

Read docs/extend/testing.md:35-46 and follow the cd filebeat step before running the documented integration-test command. Verify the command from that directory, then update the package path so the example runs successfully and confirm the documented workflow no longer fails immediately.

Written by the indexing model from the issue text.