tests: add workaround for bzr bug stable

tests: add workaround for bzr bug

This started failing for me today. I guess my bzr was upgraded.

Differential Revision: https://phab.mercurial-scm.org/D8105

--- a/tests/test-convert-bzr-directories.t	Sat Feb 01 09:14:36 2020 +0100
+++ b/tests/test-convert-bzr-directories.t	Mon Feb 10 15:50:26 2020 -0800
@@ -2,6 +2,9 @@
 
   $ . "$TESTDIR/bzr-definitions"
 
+Work around https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=944379
+  $ mkdir -p "${HOME}/.config/breezy"
+
 empty directory
 
   $ mkdir test-empty