validateQueueId does not accept underscores

### [REQUIRED] Environment info

**firebase-tools:**
Firebase Emulator

**Platform:**
Firebase CLI 14.4.0 on macOS

### [REQUIRED] Test case
```
from firebase_admin import functions
task_queue=functions.task_queue(f"locations/australia-southeast1/functions/a_b_c")

```

### [REQUIRED] Steps to reproduce

```
from firebase_admin import functions
task_queue=functions.task_queue(f"locations/australia-southeast1/functions/a_b_c")

```

### [REQUIRED] Expected behavior
This should be an acceptable queue ID.

### [REQUIRED] Actual behavior
Instead, it is throwing:
```
Error: Queue ID must start with a letter followed by up to 62 letters, numbers, hyphens, or underscores and must end with a letter or a number
```

This is due to the regex has not been updated to accomodate underscores:

https://github.com/firebase/firebase-tools/blob/d39d184eceaa33676dc951d26a1689db2a741bb7/src/emulator/tasksEmulator.ts#L194

in

https://github.com/firebase/firebase-tools/blob/d39d184eceaa33676dc951d26a1689db2a741bb7/src/emulator/tasksEmulator.ts#L185

Inspect src/emulator/tasksEmulator.ts around lines 185-194, then reproduce the issue with the provided task_queue example using the a_b_c queue ID. Done means queue IDs containing underscores are accepted while the existing validation rules remain enforced.

Written by the indexing model from the issue text.