Drop Python 3.7 support

[akihironitta]

Outline & Motivation

One of the main reasons we've supported 3.7 is, AFAIK, because Google Colab had 3.7 as its default runtime. Now that Google Colab upgraded the Python version to 3.8, we could start considering removal of our 3.7 support.

Pitch

No response

Additional context

References:

• Upgrade to Python 3.8 googlecolab/colabtools#3246
• Drop Python 3.7 support (following NEP 29) pytorch/pytorch#80513
  • Maybe, we should wait for PyTorch to drop 3.7 support first?

cc @carmocca @akihironitta @Borda @lantiga

[carmocca]

I would wait until the release after the 27th of June: https://endoflife.date/python

[akihironitta]

Sure, we can keep 3.7 until its final patch release. Just wanted to bring this up as we're free to drop the support now as we follow NEP29. https://pytorch-lightning.readthedocs.io/en/stable/versioning.html#python-support

PyTorch 2.0 plans to drop 3.7 support (pytorch/pytorch#80513 (comment)), so to me, it sounds reasonable for us to do so, too

[carmocca]

PyTorch dropped 3.7 with pytorch/pytorch#93155, so we can move forward with this.