Use icon warning for "Missing data" to avoid a clash with "Previous lesson"

aleksis/apps/alsijil/templates/alsijil/partials/lesson_status.html

@@ -14,7 +14,7 @@
   {% endif %}
 
   {% if now_dt > time_end %}
-    {% include "alsijil/partials/lesson_status_icon.html" with text=_("Missing data") icon="history" color="red" %}
+    {% include "alsijil/partials/lesson_status_icon.html" with text=_("Missing data") icon="warning" color="red" %}
   {% elif now_dt > time_start and now_dt < time_end %}
     {% include "alsijil/partials/lesson_status_icon.html" with text=_("Pending") icon="more_horiz" color="orange" %}
   {% else %}
@@ -27,7 +27,7 @@
   {% if substitution.cancelled or register_object.get_substitution.cancelled %}
     {% include "alsijil/partials/lesson_status_icon.html" with text=_("Lesson cancelled") icon="cancel" color="red" %}
   {% elif now_dt > time_end %}
-    {% include "alsijil/partials/lesson_status_icon.html" with text=_("Missing data") icon="history" color="red" %}
+    {% include "alsijil/partials/lesson_status_icon.html" with text=_("Missing data") icon="warning" color="red" %}
   {% elif now_dt > time_start and now_dt < time_end %}
     {% include "alsijil/partials/lesson_status_icon.html" with text=_("Pending") icon="more_horiz" color="orange" %}
   {% elif substitution or register_object.get_substitution %}