Use 'new' expression in places where the type is evident for content (#2590)

* Content.Client

* Content.Benchmarks

* Content.IntegrationTests

* Content.Server

* Content.Server.Database

* Content.Shared

* Content.Tests

* Merge fixes

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Shared/Alert/AlertPrototype.cs

@@ -183,7 +183,7 @@ namespace Content.Shared.Alert
         /// <returns>An alert key for the provided alert category</returns>
         public static AlertKey ForCategory(AlertCategory category)
         {
-            return new AlertKey(null, category);
+            return new(null, category);
         }
     }
 }