Update GitHub actions to Python 3.8 (#69)

* Update actions: checkout, setup-python, python

CI should probably test using the same version(s) of python that
the core modules test against.

* Enable Python 3.8 test only (#67)

Python 3.10 and 3.12 await deployment of next PySCF patch to pypi

.github/workflows/ci.yml

@@ -16,11 +16,13 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
+      matrix:
+        python-version: ["3.8"] #,"3.10","3.12"]
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-python@v2
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
         with:
-          python-version: "3.7"
+          python-version: ${{ matrix.python-version }}
       - name: Install
         run: ./.github/workflows/run_ci.sh
       - name: Test with pytest