Fix module check in _async_get_flow_handler (#99509)

We should have been checking for the module in hass.data[DATA_COMPONENTS]
and not hass.config.components as the check was ineffective if there were
no existing integrations instances for the domain which is the case for
discovery or when the integration is ignored

homeassistant/config_entries.py

@@ -2055,7 +2055,9 @@ async def _async_get_flow_handler(
     """Get a flow handler for specified domain."""
 
     # First check if there is a handler registered for the domain
-    if domain in hass.config.components and (handler := HANDLERS.get(domain)):
+    if loader.is_component_module_loaded(hass, f"{domain}.config_flow") and (
+        handler := HANDLERS.get(domain)
+    ):
         return handler
 
     await _load_integration(hass, domain, hass_config)

homeassistant/loader.py

@@ -1162,3 +1162,8 @@ def _lookup_path(hass: HomeAssistant) -> list[str]:
     if hass.config.safe_mode:
         return [PACKAGE_BUILTIN]
     return [PACKAGE_CUSTOM_COMPONENTS, PACKAGE_BUILTIN]
+
+
+def is_component_module_loaded(hass: HomeAssistant, module: str) -> bool:
+    """Test if a component module is loaded."""
+    return module in hass.data[DATA_COMPONENTS]