calendar: Vertically center align week numbers

The labels were previously aligned by using top-padding, which was
relative to font-size, and therefore didn't always align the text
correctly when font scaling was enabled.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1415

data/theme/gnome-shell-sass/widgets/_calendar.scss

@@ -170,7 +170,6 @@
     height: 1.8em;
     width: 2.3em; 
     border-radius: 2px;
-    padding: 0.5em 0 0;
     margin: 6px;
     background-color: darken($bg_color, 2%);
     color: lighten($fg_color, 5%);

js/ui/calendar.js

@@ -680,6 +680,7 @@ var Calendar = GObject.registerClass({
                                            style_class: 'calendar-day-base calendar-week-number',
                                            can_focus: true });
                 let weekFormat = Shell.util_translate_time_string(N_("Week %V"));
+                label.clutter_text.y_align = Clutter.ActorAlign.CENTER;
                 label.accessible_name = iter.toLocaleFormat(weekFormat);
                 layout.attach(label, rtl ? 7 : 0, row, 1, 1);
             }