Correct name of forceFocus data attribute

Data attributes need to be '-' separated strings
in the HTML to appear as camelCase keys in the
`.dataset` (`.data()` in jQuery) property.

This corrects the assumption that the camelCasing
would carry through from the HTML.

More info:

https://developer.mozilla.org/en-US/docs/Learn/HTML/Howto/Use_data_attributes

app/templates/views/send-test.html

@@ -17,7 +17,7 @@
   {% call form_wrapper(
     class='js-stick-at-top-when-scrolling send-one-off-form' if template.template_type != 'sms' else 'send-one-off-form',
     module="autofocus",
-    data_kwargs={'forceFocus': True}
+    data_kwargs={'force-focus': True}
   ) %}
     <div class="grid-row">
       <div class="column-two-thirds {% if form.placeholder_value.label.text == 'phone number' %}extra-tracking{% endif %}">