Use isolated_build for tox

tox.ini

@@ -1,6 +1,7 @@
 [tox]
 envlist = py{36,37,38,39}-pillow{70,71,-latest},pypy3,check
-skip_missing_interpreters = True
+skip_missing_interpreters = true
+isolated_build = true
 
 [gh-actions]
 python =
@@ -20,17 +21,13 @@ extras =
 commands = pytest --cov sigal --cov-report term tests/
 
 [testenv:check]
+skip_install = true
 deps =
-    docutils
     check-manifest
-    flake8
     collective.checkdocs
-    pygments
-usedevelop = true
 commands =
-    python setup.py checkdocs
-    python setup.py check --strict --metadata
-    check-manifest {toxinidir}
+    python setup.py check --restructuredtext
+    check-manifest -v --ignore sigal/version.py {toxinidir}
 
 [testenv:doc]
 whitelist_externals = make