update CI actions (#27)

Author: fedetaglia

.github/workflows/validate_btm.yml

@@ -8,11 +8,11 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
-    - name: Set up Python 3.9
-      uses: actions/setup-python@v1
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.12
+      uses: actions/setup-python@v5
       with:
-        python-version: 3.9
+        python-version: '3.12'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip