Add ClearProgressBar call

Fixes #9723

Author: keveleigh

Assets/MRTK/Core/Utilities/BuildAndDeploy/UnityPlayerBuildTools.cs

@@ -132,6 +132,8 @@ public static BuildReport BuildUnityPlayer(IBuildInfo buildInfo)
             // Call the post-build action, if any
             buildInfo.PostBuildAction?.Invoke(buildInfo, buildReport);
 
+            EditorUtility.ClearProgressBar();
+
             return buildReport;
         }