refactor: Change GetEventChannel method to not be virtual

Signed-off-by: André Silva <[email protected]>

Author: askpt

src/OpenFeature/FeatureProvider.cs

@@ -140,7 +140,7 @@ public virtual Task ShutdownAsync(CancellationToken cancellationToken = default)
         /// Returns the event channel of the provider.
         /// </summary>
         /// <returns>The event channel of the provider</returns>
-        public virtual Channel<object> GetEventChannel() => this.EventChannel;
+        public Channel<object> GetEventChannel() => this.EventChannel;
 
         /// <summary>
         /// Track a user action or application state, usually representing a business objective or outcome. The implementation of this method is optional.