tests: fix test-chg to ignore a warning about being unable to set locale This is apparently coming from bash when bash is providing the sh that we're using to execute the .sh file generated by run-tests for this test. Bash on my machine: ``` $ sh --version GNU bash, version 5.1.4(1)-release (x86_64-pc-linux-gnu) Copyright (C) 2020 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software; you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. $ sh sh-5.1$ LC_CTYPE=unsupported_value echo hi sh: warning: setlocale: LC_CTYPE: cannot change locale (unsupported_value): No such file or directory hi ``` Differential Revision: https://phab.mercurial-scm.org/D10468