fix RegExp named capture groups object prototype

CHANGELOG.md

@@ -21,6 +21,7 @@
 - Relaxed some specific cases of [`Number.fromString`](https://github.com/tc39/proposal-number-fromstring) validation before clarification of [proposal-number-fromstring/24](https://github.com/tc39/proposal-number-fromstring/issues/24)
 - Fixed `@@toStringTag` property descriptors on DOM collections, [#1312](https://github.com/zloirock/core-js/issues/1312)
 - Fixed the order of arguments validation in `Array` iteration methods, [#1313](https://github.com/zloirock/core-js/issues/1313)
+- Fixed `RegExp` named capture groups object prototype (should be `null`)
 - Some minor `atob` / `btoa` improvements
 - Compat data improvements:
   - [`Promise.withResolvers`](https://github.com/tc39/proposal-promise-with-resolvers) marked as shipped from FF121

packages/core-js/modules/es.regexp.constructor.js

@@ -5,6 +5,7 @@ var uncurryThis = require('../internals/function-uncurry-this');
 var isForced = require('../internals/is-forced');
 var inheritIfRequired = require('../internals/inherit-if-required');
 var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
+var create = require('../internals/object-create');
 var getOwnPropertyNames = require('../internals/object-get-own-property-names').f;
 var isPrototypeOf = require('../internals/object-is-prototype-of');
 var isRegExp = require('../internals/is-regexp');
@@ -77,7 +78,7 @@ var handleNCG = function (string) {
   var index = 0;
   var result = '';
   var named = [];
-  var names = {};
+  var names = create(null);
   var brackets = false;
   var ncg = false;
   var groupid = 0;

tests/unit-global/es.regexp.constructor.js

@@ -3,6 +3,8 @@
 import { DESCRIPTORS, GLOBAL } from '../helpers/constants.js';
 import { nativeSubclass } from '../helpers/helpers.js';
 
+const { getPrototypeOf } = Object;
+
 if (DESCRIPTORS) {
   QUnit.test('RegExp constructor', assert => {
     const Symbol = GLOBAL.Symbol || {};
@@ -80,6 +82,7 @@ if (DESCRIPTORS) {
     // eslint-disable-next-line regexp/no-unused-capturing-group -- required for testing
     assert.same(RegExp('(b)').exec('b').groups, undefined, 'NCG #2');
     const { groups } = RegExp('foo:(?<foo>\\w+),bar:(?<bar>\\w+)').exec('foo:abc,bar:def');
+    assert.same(getPrototypeOf(groups), null, 'null prototype');
     assert.deepEqual(groups, { foo: 'abc', bar: 'def' }, 'NCG #3');
     // fails in Safari
     // assert.same(Object.getPrototypeOf(groups), null, 'NCG #4');