Drop support for Python 3.7

Python 3.7 reached its end of life in 2023. I suggest dropping support.

That would mean to touch:

BERTopic/setup.py

Line 90 in e7369d0

"Programming Language :: Python :: 3.7",

and

BERTopic/setup.py

Line 106 in e7369d0

python_requires='>=3.7',

In your CI job, you test 3.8 and 3.9 anyway, not 3.7.

I am happy to submit a PR. What do you think?

Refs:

https://devguide.python.org/versions/

Ah, right. I meant to do that but totally forgot about it. Sure, let's drop it! It should also be changed in the README where it currently mentions 3.7+. Other than that, I think those were all places.

Should I submit a PR then? Happy to.

@afuetterer Thanks for the PR, I'll go ahead and merge it.