fix oidcc_plug.gen.controller AuthHTML generation and its testing

[Lionstiger]

Encountered errors when running oidcc_plug.gen.controller and found that the igniter task generates this code:
(example using test values)

# lib/test/test_web/auth_html.ex
defmodule Test.TestWeb.AuthHTML do
  defmodule Test.TestWeb.AuthHTML do
    use TestWeb, :html
    embed_templates("auth_html/*")
end 

This causes auth errors to not render at all.

This pr updates the path to lib/test_web/controllers/auth_html.ex and removed the redundant defmodule line.
Also changes the test for that module to reflect those changes.