Fix broken graphql playground (#13287)

Fixes https://github.com/twentyhq/twenty/issues/12991
Also fixes a regression on main where updateEvent are not correctly emit
when calling repository.update()

packages/twenty-server/src/engine/api/graphql/workspace-schema-builder/graphql-types/scalars/date.scalar.ts

@@ -15,6 +15,10 @@ export const DateScalarType = new GraphQLScalarType({
       return new Date(parseInt(ast.value, 10));
     }
 
+    if (ast.kind === Kind.STRING) {
+      return new Date(ast.value);
+    }
+
     return null;
   },
 });