Update changelog with #11903 merge.

debian/changelog

@@ -27,6 +27,9 @@ tails (2.7) UNRELEASED; urgency=medium
     - Fix multiarch support in Synaptic. (Closes: #11820)
     - Set default spelling language to en_US in Icedove. (Closes: #11037)
 
+  * Build system
+    - Disable debootstrap merged-usr option. (Closes: #11903)
+
   * Test suite
     - Add test for incremental upgrades. (Closes: #6309)
     - Add tests for Icedove. (Closes: #6304)