tests: accept new bzr message about switching branches

The new version apparently prints "Switched to branch at " instead of
"Switched to branch: ".

Differential Revision: https://phab.mercurial-scm.org/D8106

tests/test-convert-bzr.t

@@ -226,7 +226,7 b' Multiple branches'
   Created tag trunk-tag.
   $ bzr switch -b branch
   Tree is up to date at revision 1.
-  Switched to branch: *repo/branch/ (glob)
+  Switched to branch *repo/branch/ (glob)
   $ sleep 1
   $ echo b > b
   $ bzr add -q b
@@ -235,7 +235,7 b' Multiple branches'
   Created tag branch-tag.
   $ bzr switch --force ../repo/trunk
   Updated to revision 1.
-  Switched to branch: */repo/trunk/ (glob)
+  Switched to branch */repo/trunk/ (glob)
   $ sleep 1
   $ echo a >> a
   $ bzr ci -qm changea