worker: silence type error when calling pickle

pytype is complaining that the argument to `pickle.load()` is not an
`IO`. pytype isn't wrong: `_blockingreader` doesn't implement
`io.RawIOBase`, only `read()` and `readline()`. But it appears this is
enough for pickle. So we silence the false positive.

This fixes a regression introduced by D12304 /
cc0e059d2af8: worker: remove Python 2 support code.

Differential Revision: https://phab.mercurial-scm.org/D12337

mercurial/worker.py

@@ -279,7 +279,11 b' def _posixworker(ui, func, staticargs, a'
         while openpipes > 0:
             for key, events in selector.select():
                 try:
+                    # The pytype error likely goes away on a modern version of
+                    # pytype having a modern typeshed snapshot.
+                    # pytype: disable=wrong-arg-types
                     res = pickle.load(_blockingreader(key.fileobj))
+                    # pytype: enable=wrong-arg-types
                     if hasretval and res[0]:
                         retval.update(res[1])
                     else: