ReferenceError in settings.js for suborgs parsing

## Problem Description

The suborgs functionality is broken and the app errors out when trying to parse a file in the `.github/suborgs/` folder.

### What is actually happening

The app fails with:
```
ERROR (event): subOrgConfigs is not defined
ReferenceError: subOrgConfigs is not defined
at Settings.getSubOrgConfig (.../safe-settings/lib/settings.js:166:9)
```

This is due to line 166 having an invalid reference `return subOrgConfigs[k]` which should be `return this.subOrgConfigs[k]`. The app works correctly after making this change locally.

### What is the expected behavior

Correct parsing of the suborg yaml files.

### Error output, if available

```
ERROR (event): subOrgConfigs is not defined
ReferenceError: subOrgConfigs is not defined
at Settings.getSubOrgConfig (.../safe-settings/lib/settings.js:166:9)
```

## Context

### Are you using the hosted instance of probot/settings or running your own?

Running my own using the latest code on `main-enterprise`

### If running your own instance, are you using it with github.com or GitHub Enterprise?

GHEC

#### Version of probot/settings

Latest on `main-enterprise`

#### Version of GitHub Enterprise