Bump konnectivity-client to v0.0.28

Bump konnectivity network proxy to v0.0.28.
Includes a fix to ensure the KAS calls Close() on the egress connection.

vendor/sigs.k8s.io/apiserver-network-proxy/konnectivity-client/pkg/client/client.go

@@ -76,6 +76,7 @@ func CreateSingleUseGrpcTunnel(ctx context.Context, address string, opts ...grpc
 
 	stream, err := grpcClient.Proxy(ctx)
 	if err != nil {
+		c.Close()
 		return nil, err
 	}