mypy.ini: Move explicit_package_bases option in mypy section

It was placed in mypy.plugins.django-stubs section so it was not
taken into account.

mypy.ini

 [mypy]
 namespace_packages = True
 warn_unused_ignores = True
-
+explicit_package_bases = True
+# ^ Needed for mypy to detect py.typed from swh packages installed
+# in editable mode
 
 # support for django magic: https://github.com/typeddjango/django-stubs
 plugins = mypy_django_plugin.main
@@ -9,10 +11,6 @@ plugins = mypy_django_plugin.main
 [mypy.plugins.django-stubs]
 django_settings_module = swh.deposit.settings.testing
 
-explicit_package_bases = True
-# ^ Needed for mypy to detect py.typed from swh packages installed
-# in editable mode
-
 # 3rd party libraries without stubs (yet)
 
 [mypy-celery.*]