d/changelog: Build for buster release

Related to T3039

debian/changelog

+fossology (3.1-1~bpo10~swh+1) buster-swh; urgency=medium
+
+  * Build for buster
+
+ -- Antoine R. Dumont (@ardumont) <ardumont@softwareheritage.org>  Mon, 22 Feb 2021 12:04:19 +0100
+
 fossology (3.1-1~bpo9~swh+1) stretch-backports-swh; urgency=medium
 
   * Rebuild for stretch-backports-swh

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T3039 is now swh/infra/sysadm-environment#3039 (closed)