Run flake tests with a single version of Python

* The ruff linter and formatter and sdist-check do not depend on the
  version of Python.
* While by default mypy depends on the version of Python used to run it,
  code paths betweeen Python versions are identical, except for a couple
  exceptions irrelevant to typing. Besides testing typing within "legacy"
  code paths boudn to disappear doesn't ssem very useful.

Author: DimitriPapadopoulos

.github/workflows/ci.yml

@@ -23,7 +23,6 @@ jobs:
       fail-fast: false
       matrix:
         PYTHON:
-          - {VERSION: "3.8", NOXSESSION: "flake"}
           - {VERSION: "3.13", NOXSESSION: "flake"}
           - {VERSION: "3.13", NOXSESSION: "rust"}
           - {VERSION: "3.12", NOXSESSION: "docs", OPENSSL: {TYPE: "openssl", VERSION: "3.5.0"}}