[sensu_check] fix conditional validation of subscribers/standalone

[cwjohnston]

Description

Fix bug introduced by #538.

Motivation and Context

https://github.com/sensu/sensu-chef/pull/538 introduces a change which broke the build but somehow passed CI.

How Has This Been Tested?

Fixes existing broken test.

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.

[cwjohnston]

@gcymbalski thanks for pointing that out. How does it look now?

[gcymbalski]

Perfect!