Fix/edit hero img and cta in bo

[Stef-Rousset]

🎩 Description
The aim of this PR is to fix a bug that occurs on decidim-0.29.osp.dev, but not in local env or docker. When trying to edit a "Hero image and CTA" block in assembly landing page, the error to fix is :

ActionView::Template::Error (undefined local variable or method `parent_assembly' for #<ActionView::Base:0x000000095185c0>):
1: <% content_for :breadcrumb_context_menu do %>
2:   <div class="process-title-content-breadcrumb-container-right">
3:     <% if allowed_to? :create, :assembly, assembly: parent_assembly %>
4:       <% link = defined?(parent_assembly) ? new_assembly_path(parent_id: parent_assembly&.id) : new_assembly_path %>
5:       <%= link_to link, class: "button button__sm button__transparent process-title-content-breadcrumb-container-right-link" do %>
6:         <%= icon "add-line", class: "w-4 h-4" %>
decidim (af8d33194b3b) decidim-assemblies/app/views/layouts/decidim/admin/assemblies.html.erb:3

📌 Related Issues
Odoo card

Testing

• Go to the BO
• Go to an assembly and than to Landing page
• Click on edit button for the Hero image and CTA, and see that you can access the page without error.
• You can also check that you can add an image

[AyakorK]

LGTM ! However, maybe we should have fixed the CI in another PR, considering the number of files added !