test-check-py3-compat: don't run py2 part if $PYTHON is python3

contrib/python3-whitelist

@@ -56,6 +56,7 b' test-check-commit.t'
 test-check-execute.t
 test-check-interfaces.py
 test-check-module-imports.t
+test-check-py3-compat.t
 test-check-pyflakes.t
 test-check-pylint.t
 test-check-shbang.t

tests/test-check-py3-compat.t

@@ -3,6 +3,7 b''
   $ . "$TESTDIR/helpers-testrepo.sh"
   $ cd "$TESTDIR"/..
 
+#if no-py3k
   $ testrepohg files 'set:(**.py)' \
   > -X hgdemandimport/demandimportpy2.py \
   > -X mercurial/thirdparty/cbor \
@@ -21,6 +22,7 b''
   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
+#endif
 
 #if py3exe
   $ testrepohg files 'set:(**.py) - grep(pygments)' \