fix validation rule

Author: yaacovCR

src/validation/rules/SingleFieldSubscriptionsRule.ts

@@ -10,6 +10,7 @@ import { Kind } from '../../language/kinds.js';
 import type { ASTVisitor } from '../../language/visitor.js';
 
 import { collectFields } from '../../execution/collectFields.js';
+import type { VariableValues } from '../../execution/values.js';
 
 import type { ValidationContext } from '../ValidationContext.js';
 
@@ -31,9 +32,7 @@ export function SingleFieldSubscriptionsRule(
         const subscriptionType = schema.getSubscriptionType();
         if (subscriptionType) {
           const operationName = node.name ? node.name.value : null;
-          const variableValues: {
-            [variable: string]: any;
-          } = Object.create(null);
+          const variableValues: VariableValues = Object.create(null);
           const document = context.getDocument();
           const fragments: ObjMap<FragmentDefinitionNode> = Object.create(null);
           for (const definition of document.definitions) {