release: Finish preparation for 4.16.0

.release.cfg

@@ -5,10 +5,12 b' done = false'
 done = true
 
 [task:fixes_on_stable]
+done = true
 
 [task:pip2nix_generated]
+done = true
 
 [release]
-state = in_progress
+state = prepared
 version = 4.16.0