[Backport 7.x.x] Fixed some gcalloc in the debug window (#464)

* Fixed some GCAlloc in the debug window

# Conflicts:
#	com.unity.render-pipelines.high-definition/Runtime/Debug/VolumeDebug.cs

* Update changelog

Author: JulienIgnace-Unity

com.unity.render-pipelines.core/Editor/Debugging/DebugUIDrawer.cs

@@ -36,10 +36,12 @@ protected T Cast<T>(object o)
             where T : class
         {
             var casted = o as T;
-            string typeName = o == null ? "null" : o.GetType().ToString();
 
             if (casted == null)
+            {
+                string typeName = o == null ? "null" : o.GetType().ToString();
                 throw new InvalidOperationException("Can't cast " + typeName + " to " + typeof(T));
+            }
 
             return casted;
         }

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -67,6 +67,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed a null ref exception in static sky when the default volume profile is invalid.
 - Fixed an error about procedural sky being logged by mistake.
 - Fixed flickering of the game/scene view when lookdev is running.
+- Fixed some GCAlloc in the debug window.
 
 ### Changed
 - Rejecting history for ray traced reflections based on a threshold evaluated on the neighborhood of the sampled history.