py3: update output of check-py3-compat.py with python3

Recent work on mercurial/pure/mpatch.py made it import
mercurial.policy, and changed output of check-py3-compat.py with
python3 in test-check-py3-compat.t. But test-check-py3-compat.t isn't
yet updated.

tests/test-check-py3-compat.t

@@ -136,7 +136,7 b''
   mercurial/patch.py: error importing: <TypeError> getattr(): attribute name must be string (error at pycompat.py:*) (glob)
   mercurial/pathutil.py: error importing: <TypeError> getattr(): attribute name must be string (error at pycompat.py:*) (glob)
   mercurial/peer.py: error importing: <TypeError> getattr(): attribute name must be string (error at pycompat.py:*) (glob)
-  mercurial/pure/mpatch.py: error importing module: <ImportError> cannot import name 'pycompat' (line *) (glob)
+  mercurial/pure/mpatch.py: error importing module: <ImportError> cannot import name 'policy' (line *) (glob)
   mercurial/pure/osutil.py: error importing module: <ImportError> cannot import name 'policy' (line *) (glob)
   mercurial/pure/parsers.py: error importing module: <ImportError> No module named 'mercurial.pure.node' (line *) (glob)
   mercurial/pushkey.py: error importing: <TypeError> getattr(): attribute name must be string (error at pycompat.py:*) (glob)