tox.ini: fix testpaths

Broken recently in 307fa7a (features branch).

[ci skip] (since it apparently is not tested/used there)

tox.ini

@@ -206,7 +206,8 @@ rsyncdirs = tox.ini doc src testing
 python_files = test_*.py *_test.py testing/*/*.py
 python_classes = Test Acceptance
 python_functions = test
-testpaths = doc,testing
+# NOTE: "doc" is not included here, but gets tested explicitly via "doctesting".
+testpaths = testing
 norecursedirs = testing/example_scripts
 xfail_strict=true
 filterwarnings =