Update usages of ! is with is not (#2584)

* Update usages of ! is with is not

* Content.IntegrationTests commit

* Content.Server commit

* Content.Shared commit

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Client/GameObjects/Components/Mobs/StunnableComponent.cs

@@ -22,7 +22,7 @@ namespace Content.Client.GameObjects.Components.Mobs
         {
             base.HandleComponentState(curState, nextState);
 
-            if (!(curState is StunnableComponentState state))
+            if (curState is not StunnableComponentState state)
             {
                 return;
             }