Don't allow more recent versions of pytest-homeassistant-custom-component

Newer versions hang during unit tests due to resource exhaustion,
causing timeout failures on github.

requirements-dev.txt

@@ -1,6 +1,6 @@
 black
 isort
-pytest-homeassistant-custom-component~=0.4.5
+pytest-homeassistant-custom-component==0.4.5
 pytest
 pytest-asyncio
 pytest-cov