`enable_header_anchor = true` only works for _index.md

[Silejonu]

Only _index.md is affected by enable_header_anchor = true. Other pages don't have any anchor.

On Arch Linux, up-to-date:
hugo v0.127.0+extended linux/amd64 BuildDate=unknown

$ git submodule status
 ee549d5018a8fe105031ff7b9263824a3f0be54c themes/hugo-theme-monochrome (v3.1.0-2-gee549d5)

My hugo.toml:

baseURL = 'https://myweb.site'
languageCode = 'fr-fr'
defaultContentLanguage = "fr-fr"
title = 'My website'
theme = 'hugo-theme-monochrome'

[params]
footer = 'my footer'
enable_toc = true
enable_collapsible_toc = true
enable_site_search = true
enable_header_anchor = true
author = 'Silejonu'
enable_open_graph = false
enable_twitter_cards = false
color_scheme = 'dark'

[markup.highlight]
codeFences = false
lineNos = false
[param]
  [params.syntax_highlight]
  lib = "prism.js"
    [params.syntax_highlight.prism]
    enable_code_copy = true
    enable_line_no = true

[outputs]
home = ["HTML", "RSS", "JSON"]

My content/_index.md:

+++
title = 'Accueil'
date = 2024-06-12T11:32:24Z
type = 'list'
+++

# Header 1

# Header 1.2

## Header 2

My content/test.md:

+++
title = 'Test'
date = 2024-06-12T21:28:08Z
draft = true
header_anchor = true
+++

# Header 1

# Header 1.2

## Header 2