DEV: fix broken links in decprecated admin netlify info

docs/contributing/documentation/admins.md

@@ -105,10 +105,10 @@ To add a new site to Netlify to preview built documentation or storybooks, you n
 From here you need to update your repository to work with Netlify.
 For an example, see the following files.
 
--   [Volto `Makefile`](https://github.com/plone/volto/blob/main/Makefile), specifically the `netlify` section.
+-   [Volto `Makefile`](https://github.com/plone/volto/blob/18.0.0-alpha.31/Makefile), specifically the `netlify` section.
     This will become the command used to build docs on Netlify.
--   [Volto `requirements-docs.txt`](https://github.com/plone/volto/blob/main/requirements-docs.txt) specifies the requirements to build the docs.
--   [Volto `netlify.toml`](https://github.com/plone/volto/blob/main/netlify.toml) specifies when to build the docs, specifically only when there are changes to documentation files.
+-   [Volto `requirements-docs.txt`](https://github.com/plone/volto/blob/18.0.0-alpha.31/requirements-docs.txt) specifies the requirements to build the docs.
+-   [Volto `netlify.toml`](https://github.com/plone/volto/blob/18.0.0-alpha.31/netlify.toml) specifies when to build the docs, specifically only when there are changes to documentation files.
 
 Finally you need to configure your site in Netlify.
 You may have done some of these steps earlier, but you might need to refine them.