Avoid logging when there are no processes to wait for

guix-data-service/jobs.scm

@@ -122,8 +122,13 @@
            ;; Recurse, to check for other finished processes.
            (wait-on-processes))))
       (lambda (key . args)
-        (simple-format #t "key ~A args ~A\n"
-                       key args))))
+        (unless (and (eq? key 'system-error)
+                     (match args
+                       (("waitpid" "~A" ("No child processes") (10))
+                        #t)
+                       (_ #f)))
+          (simple-format #t "key ~A args ~A\n"
+                         key args)))))
 
   (define (kill-long-running-processes)
     (hash-map->list