use python 3.9 to test dev versions (pallets#5615)

Author: davidism

.github/workflows/tests.yaml

@@ -31,7 +31,7 @@ jobs:
           - {python: '3.8'}
           - {name: PyPy, python: 'pypy-3.10', tox: pypy310}
           - {name: Minimum Versions, python: '3.12', tox: py-min}
-          - {name: Development Versions, python: '3.8', tox: py-dev}
+          - {name: Development Versions, python: '3.9', tox: py-dev}
     steps:
       - uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4.2.1
       - uses: actions/setup-python@f677139bbe7f9c59b41e40162b753c062f5d49a3 # v5.2.0

tox.ini

@@ -3,7 +3,7 @@ envlist =
     py3{13,12,11,10,9,8}
     pypy310
     py312-min
-    py38-dev
+    py39-dev
     style
     typing
     docs