fix file name of clusterclass proposal

Author: schrej

docs/book/src/developer/architecture/controllers/cluster-topology.md

@@ -16,4 +16,4 @@ The high level workflow of ClusterTopology reconciliation is shown below.
 
 ### Additional information
 
-* See ClusterClass [proposal](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/202105256-cluster-class-and-managed-topologies.md#basic-behaviors)
+* See ClusterClass [proposal](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20210526-cluster-class-and-managed-topologies.md#basic-behaviors)

docs/book/src/tasks/experimental-features/cluster-class/change-clusterclass.md

@@ -114,7 +114,7 @@ potentially dangerous changes on those objects.
 
 </aside>
 
-For additional info see [compatibility rules](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/202105256-cluster-class-and-managed-topologies.md#clusterclass-compatibility)
+For additional info see [compatibility rules](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20210526-cluster-class-and-managed-topologies.md#clusterclass-compatibility)
 defined in the ClusterClass proposal.
 
 ## Planning ClusterClass changes

docs/book/src/tasks/experimental-features/cluster-class/index.md

@@ -8,7 +8,7 @@ ClusterClass is a powerful abstraction implemented on top of existing interfaces
 **Variable name to enable/disable the feature gate**: `CLUSTER_TOPOLOGY`
 
 Additional documentation:
-* Background information:  [ClusterClass and Managed Topologies CAEP](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/202105256-cluster-class-and-managed-topologies.md)
+* Background information:  [ClusterClass and Managed Topologies CAEP](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20210526-cluster-class-and-managed-topologies.md)
 * For ClusterClass authors:
     * [Writing a ClusterClass](./write-clusterclass.md)
     * [Changing a ClusterClass](./change-clusterclass.md)