Just look at the signature of Response::url(). It's (&self) -> &Url. This means that the URL is borrowed from self; similarly, the Url::as_str() method borrows the string representation of the Url. Hence, while you have a reference to the URL string, you can't call any other moving or mutating methods on the Response. (Response::text() takes self by value, as it's evident from its signature.)
In general, it's always advisable to start by reading the documentation (including the signature) of the methods you are calling.