Fixed issues preventing build

- html+django snippets are not parsing correctly due to script usage, replace with simple text snippets
- Fix up incorrect link added in extending_client_side

docs/extending/extending_client_side.md

@@ -213,7 +213,7 @@ For more complex widgets we can now integrate additional libraries whenever the
 
 In this example we will build a color picker widget using the [Coloris](https://coloris.js.org/) JavaScript library with support for custom widget options.
 
-First, let's start with the HTML, building on the [Django widgets](django:ref/forms/widgets) system that Wagtail supports for `FieldPanel` and `FieldBlock`. Using the `build_attrs` method, we build up the appropriate Stimulus data attributes to support common data structures being passed into the controller.
+First, let's start with the HTML, building on the [Django widgets](inv:django#ref/forms/widgets) system that Wagtail supports for `FieldPanel` and `FieldBlock`. Using the `build_attrs` method, we build up the appropriate Stimulus data attributes to support common data structures being passed into the controller.
 
 Observe that we are using `json.dumps` for complex values (a list of strings in this case), Django will automatically escape these values when rendered to avoid common causes of insecure client-side code.
 

docs/releases/5.2.md

@@ -499,7 +499,7 @@ The current approach will trigger a deprecation warning and will be removed in a
 
 #### Old
 
-```html+django
+```text
 {% load wagtailadmin_tags %}
 <script type="text/django-form-template" id="id_{{ formset.prefix }}-EMPTY_FORM_TEMPLATE">
     {% escapescript %}

docs/releases/6.0.md

@@ -318,7 +318,7 @@ window.enableDirtyFormCheck('.my-form', { alwaysDirty: true, confirmationMessage
 
 The new approach will be data attribute driven as follows.
 
-```javascript
+```text
 <form
   method="POST"
   data-controller="w-unsaved"