build-node: Increase number of build accounts.

* build-node.scm (%custom-base-services): Add 'build-accounts'.

build-node.scm

@@ -26,6 +26,7 @@
                                        (local-file "guix/keys/guix-hpc3.pub")
                                        (local-file "guix/keys/guix-hpc4.pub"))
                                  (guix-configuration-authorized-keys config)))
+                        (build-accounts 40)
 
                         ;; We have 24 to 32 cores.
                         (extra-options '("--max-jobs=4" "--cores=8"))))))