DX: update checkbashisms to v2.21.3

dev-tools/install.sh

@@ -20,7 +20,7 @@ cd "$(dirname "$0")"
 
 mkdir -p bin
 
-VERSION_CB="2.21.2"
+VERSION_CB="2.21.3"
 VERSION_SC="stable"
 
 echo λλλ checkbashisms