Set up Python in mergeback workflow

.github/actions/release-initialise/action.yml

@@ -16,9 +16,9 @@ runs:
       shell: bash
 
     - name: Set up Python
-      uses: actions/setup-python@v5
+      uses: actions/setup-python@v6
       with:
-        python-version: 3.12
+        python-version: '3.12'
 
     - name: Install dependencies
       run: |

.github/workflows/post-release-mergeback.yml

@@ -48,6 +48,9 @@ jobs:
         with:
           fetch-depth: 0  # ensure we have all tags and can push commits
       - uses: actions/setup-node@v6
+      - uses: actions/setup-python@v6
+        with:
+          python-version: '3.12'
 
       - name: Update git config
         run: |