tests: convert ParseError arguments to str on Python 3 Arguments internally are bytes. Printing the exception on Python 3 will include b'' prefixes. This test file uses a .out file, which doesn't support conditional output. The easiest way to get this to pass on Python 3 is to normalize the exception before printing so there are no b'' prefixes. Differential Revision: https://phab.mercurial-scm.org/D5793