Fix: use headline-text for block (#2629)

Author: lalver1

benefits/eligibility/templates/eligibility/start--sbmtd-agency-card.html

@@ -5,9 +5,9 @@
     {% translate "Agency card overview" %}
 {% endblock page-title %}
 
-{% block headline %}
+{% block headline-text %}
     {% translate "You selected a Reduced Fare Mobility ID transit benefit." %}
-{% endblock headline %}
+{% endblock headline-text %}
 
 {% block eligibility-item %}
     {% include "eligibility/includes/eligibility-item--identification--start--sbmtd-agency-card.html" %}