tests: adjust to the new format in pyflakes output According to the pyflakes' NEWS.rst, the default output format changed recently: 2.2.0 (2020-04-08) - Include column information in error messages So the lines now read: contrib/perf.py:149:15 undefined name 'xrange' mercurial/hgweb/server.py:427:13 undefined name 'reload' mercurial/util.py:2862:24 undefined name 'file' This is a graft of a similar fix that ended up on default. Differential Revision: https://phab.mercurial-scm.org/D8630