[epiphany] Fix back/forward button sensitivity

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 0b8f747dd884850518848162998e095d7b65ea5a
Author: Jan-Michael Brummer <jan brummer tabos org>
Date:   Mon Jun 8 18:45:07 2020 +0200

    Fix back/forward button sensitivity
    
    Fixes: https://gitlab.gnome.org/GNOME/epiphany/-/issues/1222

 src/resources/gtk/action-bar-start.ui | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/resources/gtk/action-bar-start.ui b/src/resources/gtk/action-bar-start.ui
index 878b76737..e604b9601 100644
--- a/src/resources/gtk/action-bar-start.ui
+++ b/src/resources/gtk/action-bar-start.ui
@@ -13,6 +13,7 @@
         <child>
           <object class="GtkButton" id="navigation_back">
             <property name="visible">True</property>
+            <property name="action-name">toolbar.navigation-back</property>
             <property name="valign">center</property>
             <!-- Translators: tooltip for the back button -->
             <property name="tooltip_text" translatable="yes">Go back to the previous page</property>
@@ -31,6 +32,7 @@
         <child>
           <object class="GtkButton" id="navigation_forward">
             <property name="visible">True</property>
+            <property name="action-name">toolbar.navigation-forward</property>
             <property name="valign">center</property>
             <!-- Translators: tooltip for the forward button -->
             <property name="tooltip_text" translatable="yes">Go forward to the next page</property>