[libhandy] themes: Bump the required GTK to 3.24.21

[Alexander Mikhaylenko <alexm src gnome org>]

commit 2e37d49b8b851315f3044aa53ccec67088859d76
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Aug 5 08:33:06 2020 +0200

    themes: Bump the required GTK to 3.24.21
    
    Let's ensure we use the latest and greatest stable. This didn't change
    the themes we ship.

 src/themes/parse-sass.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/themes/parse-sass.sh b/src/themes/parse-sass.sh
index c672abc6..4238e88c 100755
--- a/src/themes/parse-sass.sh
+++ b/src/themes/parse-sass.sh
@@ -13,7 +13,7 @@ fi
 SASSC_OPT="-M -t compact"
 
 : ${GTK_SOURCE_PATH:="../../../gtk"}
-: ${GTK_TAG:="3.24.20"}
+: ${GTK_TAG:="3.24.21"}
 
 if [ ! -d "${GTK_SOURCE_PATH}/gtk/theme/Adwaita" ]; then
    echo GTK sources not found at ${GTK_SOURCE_PATH}.