Bump debhelper from old 12 to 13.

Changes-By: lintian-brush
Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

debian/changelog

@@ -1,3 +1,9 @@
+dulwich (0.20.25-2) UNRELEASED; urgency=medium
+
+  * Bump debhelper from old 12 to 13.
+
+ -- Debian Janitor <janitor@jelmer.uk>  Sun, 19 Sep 2021 14:38:03 -0000
+
 dulwich (0.20.25-1) unstable; urgency=low
 
   * New upstream release.

debian/control

@@ -4,7 +4,7 @@ Priority: optional
 Maintainer: Debian Python Team <team+python@tracker.debian.org>
 Uploaders: Jelmer Vernooij <jelmer@debian.org>
 Homepage: https://www.dulwich.io/
-Build-Depends: debhelper-compat (= 12),
+Build-Depends: debhelper-compat (= 13),
                dh-python,
                git [!kfreebsd-amd64 !kfreebsd-i386],
                gnupg,