Switch tox -e vendoring, to use vendoring

tox.ini

@@ -48,16 +48,16 @@ commands =
    pre-commit run [] --all-files --show-diff-on-failure
 
 [testenv:vendoring]
+basepython = python3.8
 skip_install = True
 commands_pre =
 deps =
-    invoke
-    requests
+    vendoring == 0.2.2
     # Required, otherwise we interpret --no-binary :all: as
     # "do not build wheels", which fails for PEP 517 requirements
     pip>=19.3.1
 whitelist_externals = git
 commands =
     # Check that the vendoring is up-to-date
-    invoke vendoring.update
+    vendoring sync . -v
     git diff --exit-code