unknown(false) is not work when configuration "allowUnknown" is true

#### Support plan

* *is this issue currently blocking your project?* (yes/no): yes
* *is this issue affecting a production system?* (yes/no): yes

#### Context

* *node version*: 14.20.0
* *module version*: 17.6.0
* *environment* (e.g. node, browser, native): node
* *used with* (e.g. hapi application, another framework, standalone, ...): node
* *any other relevant information*:

#### How can we help?

Our project use version 14 before, we want to allow all fields of all object except for some fields we don't expect
For example, we want to allow field "e" of data.d only, and allow other unknown fields for data.b and even data, we use below code:
```js
const joi = require('joi');

const schema = joi.object().keys({
a: joi.string(),
b: joi.object().keys({
c: joi.string()
}),
d: joi.object().keys({
e: joi.string()
}).unknown(false)
});

const value = {
a: '123',
b: {
c: '123',
f: 123
},
d: {
e: '12',
g: 123
},
h: 123
};

const result = schema.validate(value, {
abortEarly: false,
allowUnknown: true
});

console.log(result?.error?.message);
// child "d" fails because ["g" is not allowed]
```

After we use version 17, the data pass the validation, which we do not expect.

Do you have any suggestions?