Use deadsnakes on ubuntu in CI test step

Author: mlech-reef

.github/workflows/ci.yml

@@ -106,7 +106,13 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
+      - name: Set up Python ${{ matrix.python-version }} (deadsnakes)
+        if: startsWith(matrix.os, 'ubuntu')
+        uses: deadsnakes/[email protected]  # staticx doesn't work with python installed by setup-python action
+        with:
+          python-version: ${{ env.PYTHON_DEFAULT_VERSION }}
       - name: Set up Python ${{ matrix.python-version }}
+        if: !startsWith(matrix.os, 'ubuntu')
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}