Function secrets with special characters are returned with the escape backslash

### Related issues

### [REQUIRED] Version info

**node:**14

**firebase-functions:**3.21.2

**firebase-tools:**11.1.0

**firebase-admin:**10.0.2

### [REQUIRED] Test case

Follow the steps to reproduce below for a test case

### [REQUIRED] Steps to reproduce

1) Create a new Firebase secret: TEST_SECRET with value `\\123\\123`
`firebase functions:secrets:set TEST_SECRET` and give it a value `\\123\\123`

2) Create a new Firebase config variable: TEST_SECRET with value `\\123\\123`
`firebase functions:config:set TEST_SECRET="\\123\\123"`

3) Create a function that runs with the secret, and logs both secret value and config value

```
export const test = functions
.runWith({ secrets: ['TEST_SECRET'] })
.region('europe-west1')
.https.onRequest((req, res) => {
console.log(process.env.TEST_SECRET); // \\\\123\\\\123
console.log(functions.config().TEST_SECRET); // \\123\\123
res.send('OK');
});
```

We can notice that the special characters in the secret that is saved to process.env get escaped, and the escaped characters are included as part of the returned string.

4) Access the secret via CLI: `firebase functions:secrets:access TEST_SECRET`, returned value is `\\123\\123` so the secret is stored in correct format in the secret manager

### [REQUIRED] Expected behavior

Secret accessed via process.env should act similarly to functions.config() and return the secret value without escaping

### [REQUIRED] Actual behavior

Secret value with special characters gets escaped, so a secret that is stored as `\\123\\123` is returned as `\\\\123\\\\123` from the process.env. In our case, we want to pass the secret as a basic auth password, but the secret is returned incorrectly as `\\\\123\\\\123` string.