External Version bump for alpinelinux new version string "3.21"

roles/netbootxyz/defaults/main.yml

@@ -155,8 +155,8 @@ releases:
     mirror: http://dl-cdn.alpinelinux.org
     name: Alpine Linux
     versions:
-    - code_name: v3.20
-      name: '3.20'
+    - code_name: v3.21
+      name: '3.21'
     - code_name: edge
       name: Edge (development)
   archlinux: