Explicit tests for VariationCache::getMultiple() and RenderCache::getMultiple()

Problem/Motivation

📌 Render the navigation toolbar in a placeholder Active has lots of implicit test coverage, but we should add some explicit tests, especially for VariationCache::getMultiple() and RenderCache::getMultiple()

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet