general: Fix AdwSpinner:size property being invalid
AdwSpinner no longer has the "size" property, so set the spinner size acc. to the docs:
"Use the GtkWidget:halign and GtkWidget:valign properties in combination with GtkWidget:width-request and GtkWidget:height-request for fine sizing control."
https://gnome.pages.gitlab.gnome.org/libadwaita/doc/main/class.Spinner.html
Edited by Automeris naranja