Custom Authorizer and AWS deployed stack don't have the same behavior

## Bug Report

**Current Behavior**

When using a Custom Authorizer, the behaviour of serverless-offline differs from the deployed stack on AWS.

**Sample Code**

This is where we define the function event trigger. As it's clear to see, we expect a HTTP POST on `/{stage}/dashboard/`
- file: trailingSlash/index.ts
```ts
events: [{
http: {
method: 'post',
path: 'dashboard',
cors: true,
authorizer: 'auth',
}
}]
```

Our custom authorizer **generatePolicy** method looks like this.
- file: auth/handler.js
```ts
const generatePolicy = (principalId: string, methodArn: string, role: string) => {

const allowedResources = [];
//arn:aws:execute-api:region:account-id:api-id/stage-name/HTTP-method/resource-path
const baseArn = methodArn.split(`/`, 2).join('/');

switch (role.toUpperCase()) {
case 'ADMIN':
allowedResources.push(`${baseArn}/*/*`)
break;
case 'USER':
allowedResources.push(`${baseArn}/*/dashboard/*`)
break;
default:
break;
}
const generatedPolicy = {
principalId: principalId,
policyDocument: {
Version: "2012-10-17",
Statement: [{
Action: "execute-api:Invoke",
Effect: "Allow",
Resource: [
...allowedResources,
]
}],
},
};
return generatedPolicy;
};
```

We're basically generating the following policy to someone with the role "USER":

```js
{
"principalId": "1234567890",
"policyDocument": {
"Version": "2012-10-17",
"Statement": [{
"Action": "execute-api:Invoke",
"Effect": "Allow",
"Resource": [
"arn:aws:execute-api:us-east-1:random-account-id:random-api-id/dev/*/dashboard/*"
]
}]
}
}
```

**Expected behavior/code**

When testing locally using serverless-offline, fetching the endpoint http://localhost:3000/dev/dashboard/, the response is 403 Forbidden [as the screenshot shows](https://drive.google.com/file/d/1KrdyqVYeeEqC8JhOjbrm-7mWYsrVjF50/view?usp=sharing).
But when we deploy the stack to AWS, fetching the endpoint https://RANDOM.execute-api.us-east-1.amazonaws.com/dev/dashboard/, the result is 200 ok as its seen [here](https://drive.google.com/file/d/1SKrq3V3bIV7ZRPOf7pJ6UHp2QfR8vqyb/view?usp=sharing).

**Environment**

- `serverless` version: v2.53.0
- `serverless-offline` version: v8.0.0
- `node.js` version: v12.21.0
- `OS`: Linux Mint 19.1 Tessa

**Additional context/Screenshots**

We found this issue while doing the research [The Fault in Our Stars](https://www.tenchisecurity.com/blog/thefaultinourstars), in which we explore how API Gateway Execute API Policy works under different conditions.
One researcher from our company opened the issue [1191](https://github.com/dherault/serverless-offline/issues/1191) where he indicates another incorrectly behaviour by serverless-offline regarding the way it evaluates policies. It still lacks a response to this date.