bdiff-torture: fix pyflakes warning reporting undefined name 'inst'
Looks like I got a latest version of pyflakes somehow or it's running on py3 and
it spotted this.
Differential Revision: https://phab.mercurial-scm.org/D6757
#require docutils gettext
$ $TESTDIR/check-gendoc de
checking for parse errors
Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
warning: please have a space before :hg: