Inference interface uncompatible with Python < 3.9

[lucadellalib]

Describe the bug

The new inference interface is not compatible with python<3.9. However in setup.py, we support python>=3.7. Python 3.8 is probably still one of the most used versions of Python.

Expected behaviour

Inference interface working for python>=3.7.

To Reproduce

>>> from speechbrain import inference
File ".../lib/python3.8/site-packages/speechbrain/inference/ASR.py", line 790, in StreamingASR
    ) -> tuple[list, list]:
TypeError: 'type' object is not subscriptable

Environment Details

No response

Relevant Log Output

No response

Additional Context

No response

[asumagic]

"Fixed" by #2456, but if we actually want to keep support for Python 3.8 we should actually just support it again officially and update the CI tests for it..