tests: do not change sys.path, it can break loading cext.parsers When running this tests with run-tests, the prefix would resolve mercurial.cext to the source tree and the attempt to load mercurial.cext.parsers would therefore fail since it doesn't exist in it. With the regular search path from run-tests, it is picked up from the temporary prefix correctly. Differential Revision: https://phab.mercurial-scm.org/D4910