fix: releases cache on prev and next

lib/workers/pr/changelog/source-github.js

@@ -144,7 +144,7 @@ async function getChangeLogJSON({
         const cacheMinutes = 30;
         await renovateCache.set(
           cacheNamespace,
-          getCacheKey(next.version),
+          getCacheKey(prev.version, next.version),
           release,
           cacheMinutes
         );