{% load wagtailadmin_tags %}
<ul class="tab-nav merged" role="tablist">
    {% for child in self.children %}
        <li id="tab-label-{{ child.heading|cautious_slugify }}" class="{{ child.classes|join:" " }} {% if forloop.first %}active{% endif %}"><a href="#tab-{{ child.heading|cautious_slugify }}" class="{% if forloop.first %}active{% endif %}">{{ child.heading }}</a></li>
    {% endfor %}
</ul>

<div class="tab-content">
    {% for child in self.children %}
        <section id="tab-{{ child.heading|cautious_slugify }}" class="{{ child.classes|join:" " }} {% if forloop.first %}active{% endif %}" role="tabpanel" aria-labelledby="tab-label-{{ child.heading|cautious_slugify }}">
            {{ child.render_as_object }}
        </section>
    {% endfor %}
</div>

{% load wagtailadmin_tags %}
<ul class="tab-nav merged" role="tablist">
    {% for child in self.children %}
        <li id="tab-label-{{ child.heading|cautious_slugify }}" class="{{ child.classes|join:" " }} {% if forloop.first %}active{% endif %}" role="tab" aria-controls="tab-{{ child.heading|cautious_slugify }}"><a href="#tab-{{ child.heading|cautious_slugify }}" class="{% if forloop.first %}active{% endif %}">{{ child.heading }}</a></li>
    {% endfor %}
</ul>

<div class="tab-content">
    {% for child in self.children %}
        <section id="tab-{{ child.heading|cautious_slugify }}" class="{{ child.classes|join:" " }} {% if forloop.first %}active{% endif %}" role="tabpanel" aria-labelledby="tab-label-{{ child.heading|cautious_slugify }}">
            {{ child.render_as_object }}
        </section>
    {% endfor %}
</div>

Add missing role="tab" in page editing tabs
Add missing role="tab" in page editing tabs
