Use utf-8 encoding in test-branchmap's clone call

After 75520c24feda it is printed in local encoding, i.e. "C" if not set
otherwise.

tests/test-branchmap

@@ -13,7 +13,7 echo foo > a/foo
 hg -R a ci -Am foo
 
 hgserve -R a --config web.push_ssl=False --config web.allow_push=* --encoding latin1
-hg clone http://localhost:$HGPORT1 b
+hg --encoding utf-8 clone http://localhost:$HGPORT1 b
 hg --encoding utf-8 -R b log
 echo bar >> b/foo
 hg -R b ci -m bar