Remove annoying CI warnings

[GiacomoPope]

I think upgrading to v3 is enough -- nope, I think v4

[GiacomoPope]

Hmm... I can't remove the warning:

code-format
The `python-version` input is not set. The version of Python currently in `PATH` will be used.

[tomato42]

that's because this:

kyber-py/.github/workflows/ci.yml

Lines 20 to 23 in c90c505

	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v2
	with:
	python-version: ${{ matrix.python-version }}

should be:

python-version: "3.12"

[GiacomoPope]

Thank you!