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.Shared/GameObjects/Components/Mobs/SharedCombatModeComponent.cs

@@ -39,7 +39,7 @@ namespace Content.Shared.GameObjects.Components.Mobs
         {
             base.HandleComponentState(curState, nextState);
 
-            if (!(curState is CombatModeComponentState state))
+            if (curState is not CombatModeComponentState state)
                 return;
 
             IsInCombatMode = state.IsInCombatMode;