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
configitems: use raw strings for hidden-{command,topic} items
These strings are regular expressions. The "\." needs to be
string escaped. We use raw strings to avoid doing that and the
SyntaxWarning we'd receive otherwise on Python 3.8.
Differential Revision: https://phab.mercurial-scm.org/D5822