Handle 3.13 better

tox.ini

@@ -7,7 +7,7 @@ requires =
   tox>=4
 envlist =
   # No preinstallations
-  py3{9,10,11,12,13}-none
+  py3{9,10,11,12,13,13t}-none
   # Minimum Python
   py39-{min,full}
   # x86 support range
@@ -31,6 +31,7 @@ python =
   3.11: py311
   3.12: py312
   3.13: py313
+  3.13t: py313t
 
 [gh-actions:env]
 DEPENDS =
@@ -58,14 +59,15 @@ pass_env =
   USERNAME
   # Environment variables we check for
   NIPY_EXTRA_TESTS
+  # Python variables
+  PYTHON_GIL
   # Pass user color preferences through
   PY_COLORS
   FORCE_COLOR
   NO_COLOR
   CLICOLOR
   CLICOLOR_FORCE
 set_env =
-  py313: PYTHON_GIL=0
   dev: PIP_ONLY_BINARY=numpy,scipy,h5py
   !dev: PIP_ONLY_BINARY=numpy,scipy,h5py,pillow,matplotlib
   pre,dev: PIP_EXTRA_INDEX_URL=https://pypi.anaconda.org/scientific-python-nightly-wheels/simple