Tell docs to ignore not found Credential class

* I am not sure why the docs can not find the Credential class. Feels
  like maybe I'm pointing at a stale awx_plugins.interfaces. Also kind
  of feels like sphinx is confused by this repo being named awx_plugins
  and there being another repo/package with a similarish name so it is
  searching ansible/awx_plugins instead of
  ansible/awx_plugins.interfaces

docs/conf.py

@@ -209,4 +209,5 @@
 # Ref: https://stackoverflow.com/a/30624034/595220
 nitpick_ignore = [
     # temporarily listed ('role', 'reference') pairs that Sphinx cannot resolve
+    ("py:class", "awx_plugins.interfaces._temporary_private_credential_api.Credential"),
 ]