fix: Prototype Pollution Vulnerability Affecting redoc <=2.2.0

[KsAkira10]

#2499

What/Why/How?

This PR fixes the security flaw in the "mergeObjects" function that is in this issue 2499

Reference

#2499

Tests

test('should prevent prototype pollution', () => {
        const target = {};
        const source = JSON.parse('{"__proto__": {"polluted": "yes"}}');

        mergeObjects(target, source);

        expect(({} as any).polluted).toBeUndefined();
 });

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Check yourself

• Code is linted
• Tested
• All new/updated code is covered with tests