check-config: use raw strings for regular expressions
This avoids SyntaxWarning on Python 3.8 for invalid \ escapes.
Differential Revision: https://phab.mercurial-scm.org/D5826
run-tests: use raw strings for regular expressions
Avoids SyntaxWarning due to invalid \ escape on Python 3.8.
Differential Revision: https://phab.mercurial-scm.org/D5825