Scale up debuginfod to CX21 (for more RAM)

When debuginfod processes big debug packages it can run out of memory
and get killed. Then, it gets restarted by systemd only to OOM again.

Let's try doubling the memory to ~4G.

tf-stage1/archlinux.tf

@@ -77,7 +77,7 @@ locals {
       domain      = "dashboards"
     }
     "debuginfod.archlinux.org" = {
-      server_type = "cpx11"
+      server_type = "cx21"
       domain      = "debuginfod"
     }
     "gitlab.archlinux.org" = {