py3: make test-bisect.t bytes-safe

contrib/python3-whitelist

@@ -16,6 +16,7 b' test-backout.t'
 test-backwards-remove.t
 test-basic.t
 test-bheads.t
+test-bisect.t
 test-bisect2.t
 test-blackbox.t
 test-bookmarks-current.t

tests/test-bisect.t

@@ -465,8 +465,8 b' test bisecting command'
   > from __future__ import absolute_import
   > import sys
   > from mercurial import hg, ui as uimod
-  > repo = hg.repository(uimod.ui.load(), '.')
-  > if repo['.'].rev() < 6:
+  > repo = hg.repository(uimod.ui.load(), b'.')
+  > if repo[b'.'].rev() < 6:
   >     sys.exit(1)
   > EOF
   $ chmod +x script.py