.github: upgrade python to 3.12 in actions

Author: nilfm99

.github/workflows/ffmpeg.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Setup python
         uses: actions/setup-python@v5
         with:
-          python-version: 3.8
+          python-version: 3.12
       - name: Install meson and ninja
         run: |
           python -m pip install --upgrade pip

.github/workflows/libvmaf.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Setup python
         uses: actions/setup-python@v5
         with:
-          python-version: 3.8
+          python-version: 3.12
       - name: Install meson and ninja
         run: |
           python -m pip install --upgrade pip