[py23_test] pass the sys.path as PYTHONPATH to python subprocess

Apparently I need to do that, or the child python process does not see fontTools in the path.

Another workaround woud be to ensure that fontTools is installed, at least in editable or develop mode (via `pip install -e .`). But the way we temporarily extend the PYTHONPATH in run-test.sh is less intrusive.

Lib/fontTools/misc/py23_test.py

@@ -37,7 +37,8 @@ class OpenFuncWrapperTest(unittest.TestCase):
 			with open(datafile, 'rb') as infile, \
 					tempfile.NamedTemporaryFile(delete=False) as outfile:
 				check_call(
-					[sys.executable, script], stdin=infile, stdout=outfile)
+					[sys.executable, script], stdin=infile, stdout=outfile,
+					env={"PYTHONPATH": ":".join(sys.path)})
 			result = not filecmp.cmp(infile.name, outfile.name, shallow=False)
 		finally:
 			os.remove(script)