chore: add a placeholder test so pytest doesn't complain

Author: imnotjames

tests/test_placeholder.py

@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: 2019 Damien P. George
+#
+# SPDX-License-Identifier: MIT
+#
+# MicroPython uasyncio module
+# MIT license; Copyright (c) 2019 Damien P. George
+
+
+def test_placeholder():
+    # Because we have the tests directory, the CI will attempt to run pytest
+    # and fail because no tests exist.  By adding a placeholder test that
+    # we can avoid that without having to avoid the directory name `tests`
+    pass