Description:
When the parent reference in a Route object (on both HTTPRoute and TLSRoute), is updated
to point to a non-existing gateway, the Route parent condition is not updated properly

Repro steps:

1. apply examples/kubernetes/quickstart.yaml - ensure that Gateway has proper Status conditions, with 1 listener condition
   showing attachedRoutes: 1. Ensure that the HTTPRoute also has proper Parent Condition present. The httproute parent condition might look something like this

status:
    parents:
    - conditions:
      - lastTransitionTime: "2022-12-03T07:23:33Z"
        message: Route is accepted
        observedGeneration: 1
        reason: Accepted
        status: "True"
        type: Accepted
      controllerName: gateway.envoyproxy.io/gatewayclass-controller
      parentRef:
        group: gateway.networking.k8s.io
        kind: Gateway
        name: eg

2. Now edit the HTTPRoute to point to a non-existing Gateway i.e.

parentRefs:
    - group: gateway.networking.k8s.io
      kind: Gateway
      name: eg1

Observation
While the Gateway status properly specifies the attachedRoutes: 0, the HTTPRoute on the other hand shows - what appears to be a stale parent condition. i.e.

status:
    parents:
    - conditions:
      - lastTransitionTime: "2022-12-03T07:23:33Z"
        message: Route is accepted
        observedGeneration: 1
        reason: Accepted
        status: "True"
        type: Accepted
      controllerName: gateway.envoyproxy.io/gatewayclass-controller
      parentRef:
        group: gateway.networking.k8s.io
        kind: Gateway
        name: eg

Which is the same as seen earlier.
Note that the HTTPRoute now has no mention of Gateway eg as we changed the reference to eg1, but still the Condition shows a condition that was filled earlier, while it was connected to Gateway eg.