www/varnish6: Update to 6.6.2, Fix vulnerability issue

Release notes: https://varnish-cache.org/releases/rel6.6.2.html#rel6-6-2

PR: 261562
Approved by: maintainer timeout
Security: b0c83e1a-8153-11ec-84f9-641c67a117d8
MFH: 2022Q1

(cherry picked from commit a66afb75d582849e8764d49ba29f0f0f6e6c5175)