Small reproduction for problems with concurrent inserts in cache-manager@5.

Run it:

npm ci
npm test

All tests run several concurrent inserts using Cache.wrap(). 'Concurrent' in the node.js async/ await sense on the event loop. The first test fails, when I'd expect it to succeed. Apparently, this behaviour appeared with version 5 of cache-manager. The second test succeeds, because the cache has been set explicitely before the concurrent inserts.