minor #1542 [LiveCollectionType] Fix inline rendering example (gpetraroli)

This PR was merged into the 2.x branch.

Discussion
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[LiveCollectionType] Fix inline rendering example

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| License       | MIT

Fix error in LiveCollectionType inline rendering example

Commits
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c5a36fb [LiveCollectionType] Fix inline rendering example

Author: weaverryan

src/LiveComponent/doc/index.rst

@@ -1940,7 +1940,7 @@ Inline rendering:
             {% endfor %}
 
             {# render the add button #}
-            {{ form_widget(form.comments.vars.button_add, { label: '+ Add comment', class: 'btn btn-outline-primary' }) }}
+            {{ form_widget(form.comments.vars.button_add, { label: '+ Add comment', attr: { class: 'btn btn-outline-primary' } }) }}
 
             {# render rest of the form #}
             {{ form_row(form) }}