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

Author: imnotjames

Diff for: tests/run_tests.py

@@ -25,6 +25,13 @@
 """
 
 
+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
+
+
 def get_interpreter():
     interpreter = os.getenv("MICROPY_MICROPYTHON")