[EngSys] Reduce GitHub REST API usage

Our checks have hit the GitHub API rate limit at least once:

https://github.com/Azure/azure-rest-api-specs/actions/runs/23774594830/job/69273520718

Currently, we're running at 61%, which is probably high enough to hit the limit on activity spikes:

```
[github] load: 61%, used: 4044, remaining: 10956, reset: 00:33:29
```

Mitiations:

- eliminate unnecessary triggers
- sort workflows by number of runs, see if any can be skipped
- eliminate unnecessary API calls
- load things more lazily, fail faster to avoid API calls, etc
- convert from REST to GraphQL
- separate quota