Use Version.set() instead of assigning directly

Author: humitos

readthedocs/rtd_tests/tests/test_project_symlinks.py

@@ -832,7 +832,7 @@ def test_symlink_single_version(self):
         self.assertFilesystem(filesystem)
 
     def test_symlink_single_version_missing(self):
-        self.project.versions = []
+        self.project.versions.set([])
         self.project.save()
         self.symlink = self.symlink_class(self.project)
         self.symlink.symlink_single_version()