Fix CI: remove EOL Python 3.7, update action versions

Python 3.7 reached end-of-life in June 2023 and is no longer available
on GitHub Actions runners, causing the entire matrix to fail. Replace
it with 3.11 and update checkout/setup-python actions from the
deprecated Node.js 20 versions (v2/v3) to current (v4/v5).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kevinpjones

.github/workflows/run_tests.yml

@@ -9,12 +9,12 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.7", "3.8", "3.9"]
+        python-version: ["3.8", "3.9", "3.11"]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies