Actually enforce squareness of popular tiles

This was somehow forgotten, and worked just by accident.

src/popular-tile.ui

@@ -9,6 +9,8 @@
         <property name="valign">start</property>
         <property name="shadow_type">none</property>
         <property name="height_request">180</property>
+        <property name="obey_child">False</property>
+        <property name="ratio">1.0</property>
         <child>
           <object class="GtkButton" id="button">
             <property name="visible">True</property>