www/varnish7: Update to 7.7.1, Fix vulnerability

Release notes: https://varnish-cache.org/releases/rel7.7.0.html

	 https://varnish-cache.org/releases/rel7.7.1.html

PR: 286338
PR: 287077
Security: 89c668d5-2f80-11f0-9632-641c67a117d8

Co-authored-by: Danilo G. Baio <dbaio@FreeBSD.org>