add free-threading support

Author: davidhewitt

.github/workflows/ci.yml

@@ -63,7 +63,7 @@ jobs:
       fail-fast: ${{ !contains(github.event.pull_request.labels.*.name, 'CI-no-fail-fast') }}
       matrix:
         python-version:
-          ["3.9", "3.10", "3.11", "3.12", "3.13", pypy-3.9, pypy-3.10]
+          ["3.9", "3.10", "3.11", "3.12", "3.13", "3.13t", pypy-3.9, pypy-3.10]
         platform:
           [
             {
@@ -114,7 +114,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: Quansight-Labs/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
           architecture: ${{ matrix.platform.python-architecture }}