Speed up mqtt tests (#73423)

Co-authored-by: jbouwh <jan@jbsoft.nl>
Co-authored-by: Jan Bouwhuis <jbouwh@users.noreply.github.com>

tests/components/mqtt/test_light_template.py

@@ -41,6 +41,7 @@ from homeassistant.const import (
     STATE_OFF,
     STATE_ON,
     STATE_UNKNOWN,
+    Platform,
 )
 import homeassistant.core as ha
 from homeassistant.setup import async_setup_component
@@ -90,6 +91,13 @@ DEFAULT_CONFIG = {
 }
 
 
+@pytest.fixture(autouse=True)
+def light_platform_only():
+    """Only setup the light platform to speed up tests."""
+    with patch("homeassistant.components.mqtt.PLATFORMS", [Platform.LIGHT]):
+        yield
+
+
 @pytest.mark.parametrize(
     "test_config",
     [