test-check-py3-compat: exclude thirdparty and cffi which are known to fail

Otherwise the following errors would be spilled out:

  mercurial/cffi/bdiff.py: error importing: <ImportError> cannot import
  name '_bdiff' (error at bdiff.py:*)
  mercurial/cffi/bdiffbuild.py: error importing: <ModuleNotFoundError> No
  module named 'cffi' (error at bdiffbuild.py:*)
  mercurial/cffi/mpatch.py: error importing: <ImportError> cannot import
  name '_mpatch' (error at mpatch.py:*)
  mercurial/cffi/mpatchbuild.py: error importing: <ModuleNotFoundError> No
  module named 'cffi' (error at mpatchbuild.py:*)
  mercurial/cffi/osutilbuild.py: error importing: <ModuleNotFoundError> No
  module named 'cffi' (error at osutilbuild.py:*)
  mercurial/thirdparty/concurrent/futures/_base.py: invalid syntax: invalid
  syntax (<unknown>, line *)
  mercurial/thirdparty/concurrent/futures/process.py: error importing:
  <SyntaxError> invalid syntax (_base.py, line 416) (error at __init__.py:*)
  mercurial/thirdparty/concurrent/futures/thread.py: error importing:
  <SyntaxError> invalid syntax (_base.py, line 416) (error at __init__.py:*)
  mercurial/thirdparty/zope/interface/_flatten.py: error importing:
  <ImportError> cannot import name 'Declaration' (error at _flatten.py:*)

Some of them can be suppressed by building cffi modules for example, but
I don't think it's worth keeping these modules covered by the compatibility
checker.

tests/test-check-py3-compat.t

@@ -1,39 +1,40 b''
 #require test-repo
 
   $ . "$TESTDIR/helpers-testrepo.sh"
   $ cd "$TESTDIR"/..
 
   $ testrepohg files 'set:(**.py)' \
   > -X hgdemandimport/demandimportpy2.py \
   > -X mercurial/thirdparty/cbor \
   > | sed 's|\\|/|g' | xargs $PYTHON contrib/check-py3-compat.py
   contrib/python-zstandard/setup.py not using absolute_import
   contrib/python-zstandard/setup_zstd.py not using absolute_import
   contrib/python-zstandard/tests/common.py not using absolute_import
   contrib/python-zstandard/tests/test_buffer_util.py not using absolute_import
   contrib/python-zstandard/tests/test_compressor.py not using absolute_import
   contrib/python-zstandard/tests/test_compressor_fuzzing.py not using absolute_import
   contrib/python-zstandard/tests/test_data_structures.py not using absolute_import
   contrib/python-zstandard/tests/test_data_structures_fuzzing.py not using absolute_import
   contrib/python-zstandard/tests/test_decompressor.py not using absolute_import
   contrib/python-zstandard/tests/test_decompressor_fuzzing.py not using absolute_import
   contrib/python-zstandard/tests/test_estimate_sizes.py not using absolute_import
   contrib/python-zstandard/tests/test_module_attributes.py not using absolute_import
   contrib/python-zstandard/tests/test_train_dictionary.py not using absolute_import
   setup.py not using absolute_import
 
 #if py3exe
   $ testrepohg files 'set:(**.py) - grep(pygments)' \
   > -X hgdemandimport/demandimportpy2.py \
   > -X hgext/fsmonitor/pywatchman \
-  > -X mercurial/thirdparty/cbor \
+  > -X mercurial/cffi \
+  > -X mercurial/thirdparty \
   > | sed 's|\\|/|g' | xargs python3 contrib/check-py3-compat.py \
   > | sed 's/[0-9][0-9]*)$/*)/'
 
 #endif
 
 #if py3exe py3pygments
   $ testrepohg files 'set:(**.py) and grep(pygments)' | sed 's|\\|/|g' \
   > | xargs python3 contrib/check-py3-compat.py \
   > | sed 's/[0-9][0-9]*)$/*)/'
 #endif