py3: add b'' prefixes in test-abort-checkin.t

# skip-blame because we just added a b'' prefix.

tests/test-abort-checkin.t

@@ -1,37 +1,37 b''
   $ cat > abortcommit.py <<EOF
   > from mercurial import error
   > def hook(**args):
-  >     raise error.Abort("no commits allowed")
+  >     raise error.Abort(b"no commits allowed")
   > def reposetup(ui, repo):
-  >     repo.ui.setconfig("hooks", "pretxncommit.nocommits", hook)
+  >     repo.ui.setconfig(b"hooks", b"pretxncommit.nocommits", hook)
   > EOF
   $ abspath=`pwd`/abortcommit.py
 
   $ cat <<EOF >> $HGRCPATH
   > [extensions]
   > mq =
   > abortcommit = $abspath
   > EOF
 
   $ hg init foo
   $ cd foo
   $ echo foo > foo
   $ hg add foo
 
 mq may keep a reference to the repository so __del__ will not be
 called and .hg/journal.dirstate will not be deleted:
 
   $ hg ci -m foo
   error: pretxncommit.nocommits hook failed: no commits allowed
   transaction abort!
   rollback completed
   abort: no commits allowed
   [255]
   $ hg ci -m foo
   error: pretxncommit.nocommits hook failed: no commits allowed
   transaction abort!
   rollback completed
   abort: no commits allowed
   [255]
 
   $ cd ..