Project.documentation_type is `auto`
We have 528 projects with the `Project.documentation_type` set in `auto` and this value is not allowed in the code.

This value is used, for example at: https://github.com/rtfd/readthedocs.org/blob/be4ff5b9c4fb6f8c4f8b093e98a1359491a52b1f/readthedocs/doc_builder/python_environments.py#L276

But the dictionary used to get the proper builder class doesn't have the `auto` value and make the build to fail:

https://github.com/rtfd/readthedocs.org/blob/be4ff5b9c4fb6f8c4f8b093e98a1359491a52b1f/readthedocs/doc_builder/loader.py#L15-L32

We do have a way to protect ourselves for this, but this is still happening in production.

https://github.com/rtfd/readthedocs.org/blob/be4ff5b9c4fb6f8c4f8b093e98a1359491a52b1f/readthedocs/projects/tasks.py#L429-L431

I suppose that this is still happening because of #3946 isn't deployed yet.

> This doesn't seem to be too important, but just filling this issue to keep track of this and make sure that it doesn't happen anymore after that PR is deployed.

Ref: https://sentry.io/read-the-docs/readthedocs-org/issues/472212666/events/latest/
diff --git a/readthedocs/projects/tasks.py b/readthedocs/projects/tasks.py
index d871eb0a4..1673f7374 100644
--- a/readthedocs/projects/tasks.py
+++ b/readthedocs/projects/tasks.py
@@ -548,6 +548,7 @@ class UpdateDocsTaskStep(SyncRepositoryMixin):
         project_data['documentation_type'] = ret
         api_v2.project(self.project.pk).put(project_data)
         self.project.documentation_type = ret
+        self.version.project.documentation_type = ret
 
     def update_app_instances(self, html=False, localmedia=False, search=False,
                              pdf=False, epub=False):
['readthedocs/projects/tasks.py']