chore(deps): update dependency antsibull-docs to >=2.18,<2.19 (#660)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
|
[antsibull-docs](https://redirect.github.com/ansible-community/antsibull-docs)
([changelog](https://redirect.github.com/ansible-community/antsibull-docs/tree/main/CHANGELOG.md))
| `>=2.17,<2.18` -> `>=2.18,<2.19` |
[![age](https://developer.mend.io/api/mc/badges/age/pypi/antsibull-docs/2.18.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/pypi/antsibull-docs/2.18.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/pypi/antsibull-docs/2.17.1/2.18.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/antsibull-docs/2.17.1/2.18.0?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>ansible-community/antsibull-docs (antsibull-docs)</summary>

###
[`v2.18.0`](https://redirect.github.com/ansible-community/antsibull-docs/releases/tag/2.18.0)

[Compare
Source](https://redirect.github.com/ansible-community/antsibull-docs/compare/2.17.1...2.18.0)

##### Release Summary

Feature and bugfix release.

##### Minor Changes

- Add <code>:anscollection:</code> role to allow referencing
collections. The syntax is
<code>:anscollection:\`namespace.name\`</code>, or
<code>:anscollection:\`namespace.name#what\`</code> for more specific
parts of the index page

([#&#8203;393](https://redirect.github.com/ansible-community/antsibull-docs/pull/393)).
- Extend <code>:ansplugin:</code> role to allow referencing role
entrypoints. The syntax is
<code>:ansplugin:\`namespace.name.role\_name#entrypoint\`</code>

([#&#8203;393](https://redirect.github.com/ansible-community/antsibull-docs/pull/393)).
- The <code>lint-collection-docs</code> subcommand has a new option
<code>--check-extra-docs-refs</code> that checks references to
collections in extra documentation files (<code>docs/docsite/rst</code>)
([#&#8203;392](https://redirect.github.com/ansible-community/antsibull-docs/pull/392)).
- The <code>lint-collection-docs</code>'s option
<code>--plugin-docs</code> now also checks role entrypoints for
existence
([#&#8203;392](https://redirect.github.com/ansible-community/antsibull-docs/pull/392)).

##### Deprecated Features

- The following default values for options to <code>antsibull-docs
lint-collection-docs</code> are deprecated
  and will change in antsibull-docs 3.0.0:

- <code>--plugin-docs</code> will be enabled by default; right now the
default is <code>--no-plugin-docs</code>;
- <code>--skip-rstcheck</code> will be enabled by default; right now the
default is <code>--no-skip-rstcheck</code> (note that this applies to
<code>--plugin-docs</code>, not to checking extra documentation);
- <code>--check-extra-docs-refs</code> will be enabled by default; right
now the default is <code>--no-check-extra-docs-refs</code>.

We suggested to already now explicitly state the default value if you do
not want the extra checks to be run

([#&#8203;394](https://redirect.github.com/ansible-community/antsibull-docs/pull/394)).

##### Bugfixes

- Ansible-core 2.19 now lists standard Jinja2 tests and filters as
members of <code>ansible.builtin</code> with minimal documentation, but
without a <code>name</code> field in <code>doc</code>
([#&#8203;393](https://redirect.github.com/ansible-community/antsibull-docs/pull/393)).

</details>

---

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Makefile

@@ -21,6 +21,7 @@ lint-docs: venv
 	venv/bin/antsibull-docs lint-collection-docs \
 		--plugin-docs \
 		--validate-collection-refs self \
+		--check-extra-docs-refs \
 		.
 
 clean:

requirements-dev.txt

@@ -6,4 +6,4 @@ cryptography
 
 # Development requirements
 pylint
-antsibull-docs>=2.17,<2.18
+antsibull-docs>=2.18,<2.19