Fix tox (pyupgrade requires bash)

tox.ini

@@ -109,21 +109,30 @@ commands =
 
 [testenv:format]
 description = Reformat python code using Black and isort
-# skip_install = true
 deps =
     {[testenv:check]deps}
-    pyupgrade
-allowlist_externals:
-    bash
 changedir = {toxinidir}
 commands =
-    bash -ec 'pyupgrade --py37-plus --exit-zero-even-if-changed wsgidav/*.py tests/*.py setup.py'
     ruff check --fix wsgidav tests setup.py 
     isort --profile black wsgidav tests setup.py {posargs}
     black wsgidav tests setup.py
     {[testenv:lint]commands}
 
 
+[testenv:upgrade]
+description = Upgrade Python syntax to least supported version
+deps =
+    {[testenv:format]deps}
+    pyupgrade
+allowlist_externals:
+    bash
+changedir = {toxinidir}
+commands =
+    # Needs bash-style file pattern expansion:
+    bash -ec 'pyupgrade --py37-plus --exit-zero-even-if-changed wsgidav/*.py tests/*.py setup.py'
+    {[testenv:format]commands}
+
+
 [testenv:docs]
 description = Build Sphinx documentation (output directory: docs/sphinx-build)
 changedir = docs