`cbor2.CBORDecodeError` should be a subclass of `ValueError`

### Things to check first

- [x] I have searched the existing issues and didn't find my bug already reported there

- [x] I have checked that my bug is still present in the latest release

### cbor2 version

6.0.1

### Python version

3.12

### What happened?

With the recently released `cbor2` 6.0.x, `cbor2.CBORDecodeError` is not a subclass of `ValueError`.

When using data serialization libraries like the stdlib's `json`, it is a common convention that `.loads(...)` or similar raises a subclass of `ValueError` (the passed value was incorrect). This used to work fine in `cbor2` as well until the very recent 6.0.x releases.

### How can we reproduce the bug?

Using older `cbor2` (5.x), this would have worked just fine:
```python
try:
cbor2.loads(b'\xde\xad\xbe\xef')
except ValueError:
print('Validation failed')
```

On 6.0.x, the decoding error is not caught as `ValueError`.