assign_am: mark potentially invalid am assignment more prominently

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

process/templates/process/assign_am.html

@@ -64,9 +64,9 @@ document.addEventListener("DOMContentLoaded", evt => { main(); });
           <input type="hidden" name="am" value="{{am.lookup_key}}">
           <button
           {% if am.person.status == "dd_u" and process.applying_for == "dd_nu" %}
-            class="btn btn-sm btn-secondary" title="DD_U AMs should be preferably assigned to DD_U processes"
+            class="btn btn-sm btn-secondary" data-toggle="tooltip" title="DD_U AMs should be preferably assigned to DD_U processes"
           {% elif am.person.status == "dd_nu" and process.applying_for == "dd_u" %}
-            class="btn btn-sm btn-secondary" data-toggle="tooltip" title="DD_NU AMs should not be assigned to DD_U processes"
+            class="btn btn-sm btn-danger" data-toggle="tooltip" title="DD_NU AMs should not be assigned to DD_U processes"
           {% else %}
             class="btn btn-sm btn-primary"
           {% endif %}