docs(API): Add reason to network connect 403

The 403 error might not only be raised in swarm operations. It is
also returned when the given container is already connected to the
network and is currently running. I noticed this when during the
following PR: https://github.com/containers/podman/pull/20365

Signed-off-by: Philipp Fruck <dev@p-fruck.de>

api/swagger.yaml

@@ -10084,6 +10084,7 @@ paths:
   /networks/{id}/connect:
     post:
       summary: "Connect a container to a network"
+      description: "The network must be either a local-scoped network or a swarm-scoped network with the `attachable` option set. A network cannot be re-attached to a running container"
       operationId: "NetworkConnect"
       consumes:
         - "application/json"
@@ -10095,7 +10096,7 @@ paths:
           schema:
             $ref: "#/definitions/ErrorResponse"
         403:
-          description: "Operation not supported for swarm scoped networks"
+          description: "Operation forbidden"
           schema:
             $ref: "#/definitions/ErrorResponse"
         404: