pytype: ignore certifi import error

This is an optional import so we should not complains about it.

mercurial/sslutil.py

@@ -787,7 +787,7 b' def _defaultcacerts(ui):'
     # The "certifi" Python package provides certificates. If it is installed
     # and usable, assume the user intends it to be used and use it.
     try:
-        import certifi
+        import certifi  # pytype: disable=import-error
 
         certs = certifi.where()
         if os.path.exists(certs):