Do not cache non-existent JS config files forever

Missed a spot in babel#11906. Currently if you don't have a JS config file and then add one to your project, it will not be picked up without restarting the process. Changing from caching forever to never caching when files don't exist fixes the issue.

packages/babel-core/src/config/files/configuration.js

@@ -168,7 +168,7 @@ const readConfigJS = makeStrongCache(function* readConfigJS(
   }>,
 ): Handler<ConfigFile | null> {
   if (!fs.exists.sync(filepath)) {
-    cache.forever();
+    cache.never();
     return null;
   }