Upgrade Python versions in CI

Author: michaelosthege

.github/workflows/main.yml

@@ -14,9 +14,9 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest", "windows-latest"]
-        python-version: [3.7, 3.8, 3.9]
+        python-version: ["3.8", "3.9", "3.10"]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
         path: "sunode"
     - name: Install miniconda