toctree does not consider "only" directive

Describe the bug

toctree when used in templates does not consider .. only directive.

In index.rst Use .. only to only add some documents for singlehtml builder.

In the template, using toctree, and building multi-page html, all the toc tree shows up.

Since this is a multi-page html build, should the .. only cause the toctree to only have two?

How to Reproduce

Use sphinx-quickstart to set up a project with any values.

Update source/index.rst with this toc:

.. only:: singlehtml_builder

   .. toctree::
      one

.. toctree::
   :maxdepth: 2
   :caption: Contents:

   two

Create source/one.rst and source/two.rst.
Create a custom _templates/layout.html that uses toctree():

{% extends "!layout.html" %}

{%- block sidebar1 %}
{{ super() }}
{{ toctree() }}
{% endblock %

sphinx-build html

Open build/html/index.html

Expected behavior

TOC only contains link to "two"

Your project

https://github.com/ngzhian/sphinx-repro

Screenshots

No response

OS

Linux

Python version

3.9.7

Sphinx version

4.2.0

Sphinx extensions

No response

Extra tools

No response

Additional context

No response

Reproduce the behavior from source/index.rst with the custom _templates/layout.html and its toctree() call, using sphinx-build html. Compare the generated index.html TOC against the expected single link to "two"; done means the .. only directive is respected in the template-rendered TOC.