wsgicgi: switch the default PATH_INFO back to str
It looks like everything here is meant to be str, and regressed in 687b865b95ad.
Pytype didn't flag this, but is really confused about the range of possible
types for the dictionary values, and flagged missing lower() on various types
in this area.
Differential Revision: https://phab.mercurial-scm.org/D10204