`papyri render` fails with empty template

Currently, running papyri render results in the following:

$ papyri render

  ___                    _
 | _ \__ _ _ __ _  _ _ _(_)
 |  _/ _` | '_ \ || | '_| |
 |_| \__,_| .__/\_, |_| |_|
          |_|   |__/

0.0.8
[19:32:54] INFO     going to erase /home/melissa/.papyri/html                                                                                                             render.py:1365
Rendering galleries... Done    1 items in 0.03 seconds (   35 item/s)
Rendering Examples... Done    0 items in 0.00 seconds (    0 item/s)
Copying assets Done   28 items in 0.00 seconds ( 6860 item/s)
Rendering Narrative... Done    0 items in 0.00 seconds (    0 item/s)
Traceback (most recent call last):
  File "/home/melissa/projects/papyri/papyri/render.py", line 592, in render_one
    return template.render(
           ^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'render'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/melissa/micromamba/envs/papyri/bin/papyri", line 8, in <module>
    sys.exit(app())
             ^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/typer/main.py", line 328, in __call__
    raise e
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/typer/main.py", line 311, in __call__
    return get_command(self)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/typer/core.py", line 778, in main
    return _main(
           ^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/typer/core.py", line 216, in _main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/typer/main.py", line 683, in wrapper
    return callback(**use_params)  # type: ignore
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/melissa/projects/papyri/papyri/__init__.py", line 509, in render
    trio.run(m2, ascii, html, dry_run, sidebar, graph, minify)
  File "/home/melissa/micromamba/envs/papyri/lib/python3.11/site-packages/trio/_core/_run.py", line 2093, in run
    raise runner.main_task_outcome.error
  File "/home/melissa/projects/papyri/papyri/render.py", line 1384, in main
    await html_renderer._write_api_file(
  File "/home/melissa/projects/papyri/papyri/render.py", line 772, in _write_api_file
    data = self.render_one(
           ^^^^^^^^^^^^^^^^
  File "/home/melissa/projects/papyri/papyri/render.py", line 608, in render_one
    raise ValueError("qa=", qa) from e
ValueError: ('qa=', 'numpy:savez')

It seems like this was introduced by https://github.com/jupyter/papyri/pull/319/files# (see lines 749-752), which creates an empty template for an html renderer.

More importantly: this did not fail CI - should we add at least a smoke test for rendering?

jupyter / papyri

`papyri render` fails with empty template #326