Revert "Switch to workflows without fixed version"

This reverts commit 1104626.

Author: ewinge

.github/workflows/main.yml

@@ -9,10 +9,10 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout
+      - uses: actions/checkout@v3
 
       - name: Setup Python
-        uses: actions/setup-python
+        uses: actions/setup-python@v4
         with:
           python-version: '3.10'