[gnome-calendar] window: Clean up help-overlay to use "Alt" instead of "alt"

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit bf7790862a3cbc1c56e791eb2f52637b975f4cc2
Author: Björn Daase <bjoern daase net>
Date:   Sat Feb 12 22:41:54 2022 +0100

    window: Clean up help-overlay to use "Alt" instead of "alt"

 src/gui/gtk/help-overlay.ui | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/src/gui/gtk/help-overlay.ui b/src/gui/gtk/help-overlay.ui
index ef933951..2f0319d2 100644
--- a/src/gui/gtk/help-overlay.ui
+++ b/src/gui/gtk/help-overlay.ui
@@ -47,19 +47,19 @@
             <child>
               <object class="GtkShortcutsShortcut">
                 <property name="title" translatable="yes" context="shortcut window">Go back</property>
-                <property name="accelerator">&lt;alt&gt;Left Page_Up</property>
+                <property name="accelerator">&lt;Alt&gt;Left Page_Up</property>
               </object>
             </child>
             <child>
               <object class="GtkShortcutsShortcut">
                 <property name="title" translatable="yes" context="shortcut window">Go forward</property>
-                <property name="accelerator">&lt;alt&gt;Right Page_Down</property>
+                <property name="accelerator">&lt;Alt&gt;Right Page_Down</property>
               </object>
             </child>
             <child>
               <object class="GtkShortcutsShortcut">
                 <property name="title" translatable="yes" context="shortcut window">Show today</property>
-                <property name="accelerator">&lt;alt&gt;Down &lt;Primary&gt;T Home</property>
+                <property name="accelerator">&lt;Alt&gt;Down &lt;Primary&gt;T Home</property>
               </object>
             </child>
             <child>