Use hidden directory to not interfere with discovery

Author: abravalheri

setuptools/build_meta.py

@@ -385,7 +385,8 @@ def _build_with_temp_dir(self, setup_command, result_extension,
 
         # Build in a temporary directory, then copy to the target.
         os.makedirs(result_directory, exist_ok=True)
-        with tempfile.TemporaryDirectory(dir=result_directory) as tmp_dist_dir:
+        temp_opts = {"prefix": ".tmp-", "dir": result_directory}
+        with tempfile.TemporaryDirectory(**temp_opts) as tmp_dist_dir:
             sys.argv = [
                 *sys.argv[:1],
                 *self._global_args(config_settings),