GH-1: Add mac specific configuration for live server

On Mac there are different default behaviours for multiprocessing
which is used by live server that leads to Pickling Errors.
pytest-dev/pytest-flask#104

tests/e2e/test_app.py

@@ -1,6 +1,11 @@
 import pytest
 from flask import url_for
 from playwright.sync_api import Page, expect
+import sys
+import multiprocessing
+
+if sys.platform == 'darwin':
+    multiprocessing.set_start_method("fork")
 
 
 @pytest.mark.usefixtures("live_server")