typing: suppress an import-error warning in `mercurial/utils/resourceutil.py`
Newly caught by pytype 2021-09-09.
Differential Revision: https://phab.mercurial-scm.org/D11468
To run the tests, do:cd tests/python run-tests.pySee https://mercurial-scm.org/wiki/WritingTests formore information on writing tests.