Use Python 3.13 for integration tests

[dantownsend]

Following on from: #1094

We updated everything to Python 3.13, but we can't currently install BlackSheep on Python 3.13:

Neoteroi/BlackSheep#515

So we're still running the integration tests on Python 3.12 for now:

piccolo/.github/workflows/tests.yaml

Line 43 in 265b0c2

python-version: ["3.12"]

We should change this to 3.13 once all the supported ASGI frameworks run under 3.13.

[dantownsend]

One potential solution here is to keep a dict in Piccolo which tells us which ASGI frameworks work on certain Python versions.

When someone uses piccolo asgi new we can exclude BlackSheep for now on Python 3.13, until a new release becomes available.