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%);