test: run isort in lint env

pyproject.toml

@@ -48,6 +48,7 @@ lines_after_imports = 2
 multi_line_output = 5
 include_trailing_comma = true
 use_parentheses = true
+skip_glob = ['.*']
 
 [tool.pytest.ini_options]
 testpaths = ['tests']
@@ -59,12 +60,12 @@ markers = [
 legacy_tox_ini = '''
 [tox]
 envlist =
+    lint
     py38
     py39
     py310
     py311
     py312
-    flake8
 
 [testenv]
 passenv = TEST_SHELL_*
@@ -76,9 +77,13 @@ commands = pytest {posargs}
 
 [testenv:test-ci]
 
-[testenv:flake8]
+[testenv:lint]
 basepython = python3.8
 skip_install = true
-deps = flake8
-commands = flake8
+deps =
+    flake8
+    isort
+commands =
+    flake8
+    isort -c .
 '''