PYTHON-4450 Add action testing for 3.13t

Author: ShaneHarvey

.github/workflows/test-python.yml

@@ -51,11 +51,18 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-20.04]
-        python-version: ["3.9", "pypy-3.9", "3.13"]
+        python-version: ["3.9", "pypy-3.9", "3.13", "3.13t"]
     name: CPython ${{ matrix.python-version }}-${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - name: Setup Python
+      - if: ${{ matrix.python-version == '3.13t' }}
+        name: Setup free-threaded Python
+        uses: deadsnakes/[email protected]
+        with:
+          python-version: 3.13
+          nogil: true
+      - if: ${{ matrix.python-version != '3.13t' }}
+        name: Setup Python
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}