Use Forbidden exception, not custom 403

[simonw]

Should raise datasette.utils.asgi.Forbidden, not return a custom 403

datasette-write/datasette_write/__init__.py

Lines 5 to 9 in ddd2e21

	async def write(request, datasette):
	if not await datasette.permission_allowed(
	request.actor, "datasette-write", default=False
	):
	return Response.html("Permission denied for datasette-write", status=403)

This will make it work with simonw/datasette#812