main/libretls: upgrade to 3.5.2
https://git.causal.agency/libretls/tag/?h=3.5.2
And since we also upgrade two packages in testing here:
https://ftp.openbsd.org/pub/OpenBSD/rpki-client/rpki-client-7.7.txt
https://ftp.openbsd.org/pub/OpenBSD/rpki-client/rpki-client-7.8.txt