Updated debian changelog for version 6.8.0

debian/changelog

+swh-model (6.8.0-1~swh1) unstable-swh; urgency=medium
+
+  * New upstream release 6.8.0     - (tagged by Valentin Lorentz
+    <vlorentz@softwareheritage.org> on 2023-08-21 13:26:12 +0200)
+  * Upstream changes:     - v6.8.0     - * Add discovery module
+    (imported from `swh-loader-core`)     - * Fixes to tox.ini and
+    requirements
+
+ -- Software Heritage autobuilder (on jenkins-debian1) <jenkins@jenkins-debian1.internal.softwareheritage.org>  Mon, 21 Aug 2023 11:31:07 +0000
+
 swh-model (6.7.0-1~swh1) unstable-swh; urgency=medium
 
   * New upstream release 6.7.0     - (tagged by Nicolas Dandrimont