adelie-build-txz: Use dash as /bin/sh for mini roots

adelie-build-txz

@@ -114,7 +114,7 @@ install_pkgs() {
 	header "Installing base system to tar root..."
 
 	if test -n "${MINI+mini}"; then
-		declare -r PACKAGES="adelie-core"
+		declare -r PACKAGES="adelie-core dash-binsh"
 		declare -r ARCH_PKGS=""
 	else
 		declare -r PACKAGES=$(cat packages 2>/dev/null || fatal 'No core packages specified')