GitHub Actions: Add free threaded Python 3.14t

Author: cclauss

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13', '3.14']
+        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13', '3.14', '3.14t']
 
     steps:
     - uses: actions/checkout@v5