Fix CI jobs, supported Python versions, and update checkout/setup-python actions (#51)

Python version updates:
- Add Python 3.13: already supported in the cibuildwheel job, so add to
  tests.yml in CI as well.
- Drop support for obsolete Python 3.6 and 3.7 versions. They are no longer
  even installable in CI with `setup-python`, and are far beyond their EOL
  date.
- Update the trove classifiers in `setup.py` to match.

This fixes a number of broken jobs in `tests.yml`:
- the 3.6 and 3.7 jobs were no longer working due to Python version too old
  and no longer installing
- the `windows-2019` and `ubuntu-20.04` runner images are deprecated and are
  being phased out with intermittent outages

In addition, it bumps `actions/checkout` and `actions/setup-python` to
the most recent stable releases, which is generally useful and needed for
Python 3.13 support.

Author: rgommers

.github/workflows/tests.yml

@@ -24,20 +24,22 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python_version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
-        include:
-          - os: windows-2019
-            python_version: "3.6"
-          - os: ubuntu-20.04
-            python_version: "3.6"
+        python_version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
+        exclude:
+          # The 3.9/3.10 arm64 Python binaries that `setup-python` tries to use
+          # don't work on macOS 15 anymore, so skip those.
+          - os: macos-latest
+            python_version: "3.9"
+          - os: macos-latest
+            python_version: "3.10"
     runs-on: ${{ matrix.os }}
 
     steps:
       - name: Check out repo
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Configure Python version
-        uses: actions/setup-python@v4
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python_version }}
           architecture: x64

setup.py

@@ -111,18 +111,11 @@ def setup_package():
                 "Operating System :: MacOS :: MacOS X",
                 "Operating System :: Microsoft :: Windows",
                 "Programming Language :: Cython",
-                "Programming Language :: Python :: 2.6",
-                "Programming Language :: Python :: 2.7",
-                "Programming Language :: Python :: 3.3",
-                "Programming Language :: Python :: 3.4",
-                "Programming Language :: Python :: 3.5",
-                "Programming Language :: Python :: 3.6",
-                "Programming Language :: Python :: 3.7",
-                "Programming Language :: Python :: 3.8",
                 "Programming Language :: Python :: 3.9",
                 "Programming Language :: Python :: 3.10",
                 "Programming Language :: Python :: 3.11",
                 "Programming Language :: Python :: 3.12",
+                "Programming Language :: Python :: 3.13",
                 "Topic :: Scientific/Engineering",
             ],
             cmdclass={"build_ext": build_ext_subclass},