Mark Tails 4.0~beta2 as released.

debian/changelog

-tails (4.0~beta2) UNRELEASED; urgency=medium
+tails (4.0~beta2) unstable; urgency=medium
 
   * All changes included in Tails 3.16, see the corresponding changelog entry.
 
@@ -88,7 +88,7 @@ tails (4.0~beta2) UNRELEASED; urgency=medium
     - Drop useless code based on wrong assumptions (refs: #13470).
     - Make the "I set an administration password" step more robust.
 
- -- Tails developers <tails@boum.org>  Mon, 02 Sep 2019 16:53:33 +0000
+ -- Tails developers <tails@boum.org>  Mon, 02 Sep 2019 19:55:24 +0000
 
 tails (4.0~beta1) unstable; urgency=medium