[ci] Add free threaded python interpreter 3.14t to pytest action

Author: fjosw

.github/workflows/pytest.yml

@@ -17,7 +17,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"]
         include:
           - os: macos-latest
             python-version: "3.12"