package/squid: security bump to version 5.6

Fix CVE-2021-46784: In Squid 3.x through 3.5.28, 4.x through 4.17, and
5.x before 5.6, due to improper buffer management, a Denial of Service
can occur when processing long Gopher server responses.

https://github.com/squid-cache/squid/security/advisories/GHSA-f5cp-6rh3-284w



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>