The rest of the message after running a scan should answer the question:
“The core files scan will not be run because this version of WordPress is not currently indexed by Wordfence. This may be due to using a prerelease version or because the servers are still indexing a new release. If you are using an official WordPress release, this issue will automatically dismiss once the version is indexed and another scan is run.”
It’s unfortunate that Wordfence did not index the new version before release as usual. My inbox is now filling with Wordfence Alerts, and clients are calling with questions because some of them also receive the alerts.