Install 3.13 from deadsnakes

Author: andfoy

.github/workflows/main.yml

@@ -19,15 +19,21 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: actions/setup-python@v5
-        if: ${{ !endsWith(matrix.python-version, 't') }}
+        if: ${{ !endsWith(matrix.python-version, 't') && matrix.python-version != '3.13' }}
         with:
           python-version: ${{ matrix.python-version }}
 
-      - uses: deadsnakes/action@6c8b9b82fe0b4344f4b98f2775fcc395df45e494 # v3.1.0
+      - name: Setup free-threaded variables
         if: ${{ endsWith(matrix.python-version, 't') }}
+        run: |
+          echo "FREE_THREADED=1" >> "$GITHUB_ENV"
+          echo "PYTHON_GIL=0" >> "$GITHUB_ENV"
+
+      - uses: deadsnakes/action@6c8b9b82fe0b4344f4b98f2775fcc395df45e494 # v3.1.0
+        if: ${{ endsWith(matrix.python-version, 't') || matrix.python-version == '3.13' }}
         with:
           python-version: "3.13"
-          nogil: true
+          nogil: ${{ env.FREE_THREADED == '1' }}
 
       - name: Install tox
         run: pip install tox