Upgrade snok/install-poetry to v1.3.4 to fix Python 3.8 on Windows …

…issue

See: snok/install-poetry#94

.github/workflows/testing.yml

@@ -21,7 +21,7 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
-      - uses: snok/install-poetry@v1.3.2
+      - uses: snok/install-poetry@v1.3.4
       - name: Install dependencies
         run: poetry install
       - uses: FedericoCarboni/setup-ffmpeg@v3