dropdown: Make search entry shrink

We don't want the popup to be wider than the button
if we can help it. The search entry does not need
to be very wide.

gtk/ui/gtkdropdown.ui

@@ -59,6 +59,8 @@
             <signal name="search-changed" handler="search_changed"/>
             <signal name="stop-search" handler="search_stop"/>
             <property name="visible">0</property>
+            <property name="max-width-chars">6</property>
+            <property name="width-chars">6</property>
             <property name="placeholder-text" translatable="yes">Search…</property>
           </object>
         </child>