docs: fix mkdocs build

[mloiseleur]

What does it do ?

Fix mkdocs configuration on README.md and chart CHANGELOG.md that was broken since this PR and triggered by this other PR.

Motivation

Build with mkdocs failed with this error:

WARNING -  [macros] - ERROR # _Macro Syntax Error_

           _File_: `README.md`

           _Line 162 in Markdown file:_ **Missing end of comment tag**
           ```markdown
           - [v0.10.0](https://github.com/kubernetes-sigs/external-dns/releases/tag/v0.10.0): use of `networking.k8s.io/ingresses` instead of
           `extensions/ingresses` (see [#2281](https://github.com/kubernetes-sigs/external-dns/pull/2281))
           ```

WARNING -  [macros] - ERROR # _Macro Syntax Error_

           _File_: `charts/external-dns/CHANGELOG.md`

           _Line 23 in Markdown file:_ **Missing end of comment tag**
           ```markdown
           - Add option to configure `annotationFilter` via dedicated chart value. ([#5737](https://github.com/kubernetes-sigs/external-dns/pull/5737))
           _@dshatokhin_
           ```

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Raffo

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• OWNERS [Raffo]

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[ivankatliarchuk]

/lgtm