feat: one more try building freethreaded python

Author: vinitkumar

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py310, py311, py312, py313, pypy310, pypy311, py314-full
+envlist = py310, py311, py312, py313, py313t, pypy310, pypy311, py314-full
 
 [testenv]
 deps =
@@ -10,3 +10,9 @@ allowlist_externals = pytest
 
 commands =
     pytest --cov --cov-report=xml
+
+[testenv:py313t]
+description = Python 3.13 free threaded environment
+basepython = python3.13t
+deps = {[testenv]deps}
+commands = {[testenv]commands}