add no diff step
Created by: davejrt
Adds a very crude step to avoid empty pipelines trying to be uploaded if a user changes a file we don't yet capture by another linter eg: https://github.com/sourcegraph/sourcegraph/pull/40218
Current error:
2022-08-10 16:43:09 WARN POST https://agent.buildkite.com/v3/jobs/018288a2-e0a3-4613-a6b9-4f62910c871b/pipelines: 422 The `steps` property is required for a group (Attempt 0/60 Retrying in -2562047h47m11.854775807s)
--
| 2022-08-10 11:43:09 CST | 2022-08-10 16:43:09 ERROR Unrecoverable error, skipping retries
| 2022-08-10 11:43:09 CST | 2022-08-10 16:43:09 FATAL Failed to upload and process pipeline: POST https://agent.buildkite.com/v3/jobs/018288a2-e0a3-4613-a6b9-4f62910c871b/pipelines: 422 The `steps` property is required for a group
| 2022-08-10 11:43:09 CST | 🚨 Error: The command exited with status 1
Test plan
https://buildkite.com/sourcegraph/sourcegraph/builds/166470#01828a3a-5687-4ae8-b0bf-c91797492e94