Fix middleware doc example

[ajoga]

I'm starting to use the project with the newly release 3 version.

connexion/docs/middleware.rst

Lines 115 to 120 in 70084bc

	from connexion import AsyncApp, ConnexionMiddleware
	middlewares = [middleware for middleware in ConnexionMiddleware.default_middlewares
	if not isinstance(middleware, SecurityMiddleware)]
	app = AsyncApp(__name__, middlewares=middlewares)

It seems this example is not correct.

1. missing import for SecurityMiddleware
2. ConnexionMiddleware.default_middlewares is a list of classes, not class instances: the filtering never happen.

[RobbeSneyders]

Thanks @ajoga!

[coveralls]

coverage: 94.271%. remained the same
when pulling 9ed6e29 on ajoga:middlewaredocs
into 70084bc on spec-first:main.