run-tests: find python binary on Python 3 (
issue6361)
Return strings from _findprogram as all callers expect
unicode strings.
Previously the check in _usecorrectpython agains sysexecutable
was always false on Python 3.
Differential Revision: https://phab.mercurial-scm.org/D8674
tests: ignore possible diagnostics from gpg 2.2
Differential Revision: https://phab.mercurial-scm.org/D8672