varnish:6 security update

Varnish Cache is a high-performance HTTP accelerator. It stores web pages in
memory so web servers don't have to create the same web page over and over
again, giving the website a significant speed up.

Security Fix(es):

HTTP/2: Multiple HTTP/2 enabled web servers are vulnerable to a DDoS attack
(Rapid Reset Attack) (CVE-2023-44487)

For more details about the security issue(s), including the impact, a CVSS
score, acknowledgments, and other related information, refer to the CVE page(s)
listed in the References section.

CVE(s):
CVE-2023-44487

Modularity name: varnish
Stream name: 6