Fix page title to match H1 on create API key page

The page `<title>` was using previous wording.

app/templates/views/api/keys/create.html

@@ -4,7 +4,7 @@
 {% from "components/radios.html" import radios %}
 
 {% block page_title %}
-  Add a new API key – GOV.UK Notify
+  Create an API key – GOV.UK Notify
 {% endblock %}
 
 {% block maincolumn_content %}