security/gnutls: Update to 3.7.7

ChangeLog: https://lists.gnupg.org/pipermail/gnutls-help/2022-July/004746.html
PR: 265726
Approved by: tijl (maintainer)
MFH: 2022Q3
Security: CVE-2022-2509

(cherry picked from commit 5b45bb04f59989cae4ade5cd99ef40873b97370b)