Mark Tails 4.3 as released.

debian/changelog

-tails (4.3) UNRELEASED; urgency=medium
+tails (4.3) unstable; urgency=medium
 
   * Security fixes
     - Upgrade Tor Browser to 9.0.5-build2 (Closes: #17469).
@@ -76,7 +76,7 @@ tails (4.3) UNRELEASED; urgency=medium
         they need to filter out this known problem, which takes time
         and trains us to ignore problems.
 
- -- Tails developers <tails@boum.org>  Mon, 10 Feb 2020 11:13:09 +0100
+ -- Tails developers <tails@boum.org>  Mon, 10 Feb 2020 14:08:59 +0100
 
 tails (4.2.2) unstable; urgency=medium