Use querysets from the class not from an instance

When filtering using `public` and using a user,
the queryset hit this

https://github.com/rtfd/readthedocs.org/blob/45df7fd0da44be9eab3c0cb2888f6a9a15421fc5/readthedocs/builds/querysets.py#L22-L24

When the user is authenticated, we call to `get_objects_for_user`
which gets all the versions from all the user's projects.
Overriding any previous filter (`project.versions` in this case)

We don't see this in production because we serve from another domain.
And we don't see this in the corporate site because we override the
serve_docs view.

Fix readthedocs#4350
Closes readthedocs#4356

Author: stsewd

readthedocs/api/v2/views/footer_views.py

@@ -25,7 +25,7 @@ def get_version_compare_data(project, base_version=None):
     :param base_version: We assert whether or not the base_version is also the
                          highest version in the resulting "is_highest" value.
     """
-    versions_qs = project.versions.public().filter(active=True)
+    versions_qs = Version.objects.public(project=project)
 
     # Take preferences over tags only if the project has at least one tag
     if versions_qs.filter(type=TAG).exists():

readthedocs/core/views/serve.py

@@ -202,7 +202,11 @@ def serve_docs(
     if not version_slug:
         version_slug = project.get_default_version()
     try:
-        version = project.versions.public(request.user).get(slug=version_slug)
+        version = (
+            Version.objects
+            .public(user=request.user, project=project)
+            .get(slug=version_slug)
+        )
     except Version.DoesNotExist:
         # Properly raise a 404 if the version doesn't exist (or is inactive) and
         # a 401 if it does
@@ -409,8 +413,10 @@ def changefreqs_generator():
 
         if project.translations.exists():
             for translation in project.translations.all():
-                translation_versions = translation.versions.public(
-                    ).values_list('slug', flat=True)
+                translation_versions = (
+                    Version.objects.public(project=translation)
+                    .values_list('slug', flat=True)
+                )
                 if version.slug in translation_versions:
                     href = project.get_docs_url(
                         version_slug=version.slug,