Reword title of screen 4 of broadcast tour

We want to emphasise the difference over the similarity.

app/templates/views/broadcast/tour/4.html

@@ -3,7 +3,7 @@
 {% extends "admin_template.html" %}
 
 {% block per_page_title %}
-  An alert looks a bit like a text message.
+  An alert is not a normal text message.
 {% endblock %}
 
 {% set mainClasses = "govuk-!-padding-top-0 govuk-!-padding-bottom-0" %}
@@ -14,7 +14,7 @@
     <div class="govuk-grid-row">
       <div class="govuk-grid-column-one-half">
         <h1 class="heading-medium">
-          An alert looks a bit like a text message.
+          An alert is not a normal text message.
         </h1>
         <p class="govuk-body heading-medium">
           It’s broadcast directly from a mobile phone mast, so you don’t