Fix key change advisory style in dark theme

Override the light font color which is the default in dark mode.
For regular android theme this should cause no change.

stylesheets/_conversation.scss

@@ -628,6 +628,7 @@ li.entry .error-icon-container {
     display: inline-block;
     padding: 5px 10px;
     background: #fff5c4;
+    color: $grey_d;
     border-radius: $border-radius;
   }
 }