fix depreciation warnings on github actions using node12

Author: sjpb

.github/workflows/ci.yml

@@ -71,12 +71,12 @@ jobs:
 
     steps:
       - name: Check out the codebase.
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Set up Python 3.
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
-          python-version: '3.x'
+          python-version: '3.9'
 
       - name: Install test dependencies.
         run: |
@@ -104,12 +104,12 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: Check out the codebase.
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Set up Python 3.
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v4
         with:
-          python-version: '3.x'
+          python-version: '3.9'
 
       - name: Install test dependencies.
         run: |