mail/fetchmail: security update to 6.4.22.rc2

MFH: 2021Q3
URL: https://www.fetchmail.info/fetchmail-SA-2021-02.txt
Changelog: https://gitlab.com/fetchmail/fetchmail/-/blob/SNAPSHOT_6-4-22-rc2/NEWS#L87
Security: CVE-2021-39272
Security: 1d6410e8-06c1-11ec-a35d-03ca114d16d6
PR: 258071
Approved by: Corey Halpin (maintainer)