Javascript Typescript 通过动态键访问和分配对象属性

我试图通过使用keyof TestInterface类型的动态键访问TestInterface类型的对象，将一个值从TestInterface类型的对象分配给另一个TestInterface类型的对象.然而，typescript似乎忘记了这两个实例上的键是相同的，因此抛出了一个错误.

由于这句话很难读，下面是一个例子:

interface TestInterface {
    testKey?: NestesOptInterface;
    optKey?: string;
}

interface NestesOptInterface {
    key1?: string;
    key2?: string
}

const myObj : TestInterface= {

}

const myObj2 : TestInterface = {
    testKey: {
        key1: "test",
    }
}

const attributes : string[] = ['testKey', 'optKey']

const myTestKey: keyof TestInterface = attributes[0] as keyof TestInterface

/**Type 'string | NestesOptInterface | undefined' is not assignable to type '(NestesOptInterface & string) | undefined'.
 * Type 'NestesOptInterface' is not assignable to type 'NestesOptInterface & string'.
 * Type 'NestesOptInterface' is not assignable to type 'string'.(2322)**/
myObj[myTestKey] = myObj2[myTestKey]

//does work (obviously)
myObj['testKey'] = myObj2['testKey']

棘手的是，myTestKey赋值中的testKey实际上应该是字符串类型的任何值.

我想知道这是否是一个错误，或者我如何才能正确地做到这一点？这是Typescript Playground的链接.