release: Finish preparation for 4.13.1

.release.cfg

@@ -11,6 +11,7 b' done = true'
 done = true
 
 [task:pip2nix_generated]
+done = true
 
 [task:changelog_updated]
 done = true
@@ -19,7 +20,7 b' done = true'
 done = true
 
 [release]
-state = in_progress
+state = prepared
 version = 4.13.1
 
 [task:updated_translation]