Communicate runtime check eligibility to users

[swissspidy]

In order to perform runtime checks, a few conditions must be met:

• Plugin Check must be "initialized early" (using WP-CLI I presume) OR the object-cache drop-in must exist
• AND the plugin under test must be active

This is not communicated at all when running Plugin Check either via WP-CLI or in WordPress admin.

If the plugin is not active, then the runtime checks will simply not be run, without you ever noticing it.