Pending API responses get cached for too long

[dd32]

Issue Overview

When requesting a report for a specific version of a plugin, if Tide doesn't yet have a report for it it'll start to generate one and return a <p>pending</p> response.

That response then gets cached, and will return the <p>pending</p> response until it expires.
Suffixing a ?1 to the URL to bypass the URL caching then results in being able to access it.

Steps to Reproduce (for bugs)

1. Request /api/tide/v1/audit/wporg/plugin/$slug/$version for an old version of a random plugin
2. Hopefully observe a report-not-yet-generated page
3. Reload it a few minutes later, get the same pending report.
4. Suffix a cache-buster such as ?1 to the URL and see the report.

[jeffpaul]

@dd32 thanks for the feedback on this one, is there a recommended length to expire the cache that's used for things on the plugin repo that we can mirror for Tide?

[kkoppenhaver]

PR for this is here: wptide/wporg-tide-api#6