htpdate pool 2: replace fragile thepiratebay.org with www.gnome.org

thepiratebay.org is regularly broken. Even when it works, it can be blocked by
the local ISP (at the DNS or TCP/IP level), which can impact both production
Tails usage and local test suite runs (#18529).

Let's instead use a more reliable website: www.gnome.org currently
points to 3 IP addresses hosted in OpenShift containers.