GMUClusterRendererDelegate renderer not working for updating cluster image

#### Environment details

1. GMUClusterRendererDelegate
2. OS: iOS 15
3. Google Map 8.4 and Google Map Utils SDK 5.0
#### Steps to reproduce

1. Download the iOS Utils Sample App
2. Apply the renderer willRenderMarker function of the GMUClusterRendererDelegate into the ClusteringViewController

#### Code example

```
import GoogleMaps
import UIKit
import GoogleMapsUtils

/// Point of Interest Item which implements the GMUClusterItem protocol.
class POIItem: NSObject, GMUClusterItem {
var position: CLLocationCoordinate2D
var name: String!

init(position: CLLocationCoordinate2D, name: String) {
self.position = position
self.name = name
}
}

let kClusterItemCount = 10000
let kCameraLatitude = -33.8
let kCameraLongitude = 151.2

class ClusteringViewController: UIViewController, GMSMapViewDelegate, GMUClusterRendererDelegate {

private var mapView: GMSMapView!
private var clusterManager: GMUClusterManager!

override func loadView() {
let camera = GMSCameraPosition.camera(withLatitude: kCameraLatitude,
longitude: kCameraLongitude, zoom: 10)
mapView = GMSMapView.map(withFrame: CGRect.zero, camera: camera)
self.view = mapView
}

override func viewDidLoad() {
super.viewDidLoad()

// Set up the cluster manager with default icon generator and renderer.
let iconGenerator = GMUDefaultClusterIconGenerator()
let algorithm = GMUNonHierarchicalDistanceBasedAlgorithm()
let renderer = GMUDefaultClusterRenderer(mapView: mapView, clusterIconGenerator: iconGenerator)
clusterManager = GMUClusterManager(map: mapView, algorithm: algorithm, renderer: renderer)

// Register self to listen to GMSMapViewDelegate events.
clusterManager.setMapDelegate(self)

// Generate and add random items to the cluster manager.
generateClusterItems()

// Call cluster() after items have been added to perform the clustering and rendering on map.
clusterManager.cluster()
}

// MARK: - GMUMapViewDelegate

func mapView(_ mapView: GMSMapView, didTap marker: GMSMarker) -> Bool {
mapView.animate(toLocation: marker.position)
if let _ = marker.userData as? GMUCluster {
mapView.animate(toZoom: mapView.camera.zoom + 1)
NSLog("Did tap cluster")
return true
}
NSLog("Did tap marker")
return false
}

// MARK: - Private

/// Randomly generates cluster items within some extent of the camera and adds them to the
/// cluster manager.
private func generateClusterItems() {
let extent = 0.2
for _ in 1...kClusterItemCount {
let lat = kCameraLatitude + extent * randomScale()
let lng = kCameraLongitude + extent * randomScale()
let position = CLLocationCoordinate2D(latitude: lat, longitude: lng)
let marker = GMSMarker(position: position)
clusterManager.add(marker)
}
}

/// Returns a random value between -1.0 and 1.0.
private func randomScale() -> Double {
return Double(arc4random()) / Double(UINT32_MAX) * 2.0 - 1.0
}

func renderer(_ renderer: GMUClusterRenderer, willRenderMarker marker: GMSMarker) {
if let cluster = marker.userData as? GMUCluster {
print("Current cluster size: \(cluster.count)")
marker.icon = createClusterIcon(size: Int(cluster.count))
}
}

func createClusterIcon(size: Int) -> UIImage {

let clusterSize: CGFloat = 40
let renderer = UIGraphicsImageRenderer(size: CGSize(width: clusterSize, height: clusterSize))

let image = renderer.image { context in

UIColor(red: 0.13, green: 0.59, blue: 0.95, alpha: 1.0).setFill()
UIBezierPath(arcCenter: CGPoint(x: clusterSize / 2, y: clusterSize / 2), radius: clusterSize / 2, startAngle: 0, endAngle: .pi * 2, clockwise: true).fill()


// Draw cluster count text
let text = String(size)
let attributes: [NSAttributedString.Key: Any] = [
.font: UIFont.boldSystemFont(ofSize: 16),
.foregroundColor: UIColor.white
]

let textSize = text.size(withAttributes: attributes)
let textPoint = CGPoint(
x: (clusterSize - textSize.width) / 2,
y: (clusterSize - textSize.height) / 2
)
text.draw(at: textPoint, withAttributes: attributes)
}


return image
}
}
```
#### Expect Result
Cluster with icon blue circle and cluster size text to display. Print function run when icon display

#### Actual Result
Cluster still use the default cluster icon.