Revert "First attempt at tomlifying tox (#173)"

This reverts commit b6f3b8b.

pyproject.toml

@@ -140,17 +140,6 @@ overrides."tool.coverage.paths.source".inline_arrays = false
 overrides."tool.ruff.lint.isort.section-order".inline_arrays = false
 
 [tool.tox]
-env_list = [
-    "py310-linux",
-    "py310-macos",
-    "py310-windows",
-    "py311-linux",
-    "py311-macos",
-    "py311-windows",
-    "py312-linux",
-    "py312-macos",
-    "py312-windows",
-]
 legacy_tox_ini = """
     [gh-actions]
     python =
@@ -163,9 +152,13 @@ legacy_tox_ini = """
         ubuntu-latest: linux
         macos-latest: macos
         windows-latest: windows
+
+    [testenv]
+    commands =
+        pytest --cov --cov-report=lcov
+    deps =
+        pytest-cov
+
+    [tox]
+    env_list = py{310,311,312}-{linux,macos,windows}
 """
-env.testenv = {commands = [
-    "pytest --cov --cov-report=lcov",
-], deps = [
-    "pytest-cov",
-]}