Test workaround: use a custom pytest-homeassistant-custom-component

Until https://github.com/home-assistant/core/issues/69724 is fixed, use
a custom version of the plugin (which is auto generated from homeassistant,
so the author does not want to fix it there if avoidable).

.github/workflows/tests.yml

@@ -1,6 +1,6 @@
 name: Python tests
 
-on: workflow_dispatch
+on: [workflow_dispatch, pull_request, push]
 
 jobs:
   tests:

requirements-dev.txt

@@ -1,6 +1,6 @@
 black
 isort
-pytest-homeassistant-custom-component~=0.8.4
+git+https://github.com/make-all/pytest-homeassistant-custom-component@master#egg=pytest-homeassistant-custom-component
 pytest
 pytest-asyncio
 pytest-cov