test: mask rc.local generator, broken on Jammy

On jammy it started to fail, it's not really needed and we install
an empty stub anyway, so just mask the generator

(cherry picked from commit 565916c)

Author: bluca

test/test-functions

@@ -1927,13 +1927,9 @@ check_result_qemu_unittests() {
 }
 
 create_rc_local() {
-    dinfo "Create rc.local"
-    mkdir -p "${initdir:?}/etc/rc.d"
-    cat >"$initdir/etc/rc.d/rc.local" <<EOF
-#!/usr/bin/env bash
-exit 0
-EOF
-    chmod 0755 "$initdir/etc/rc.d/rc.local"
+    dinfo "Mask rc.local generator"
+    mkdir -p "${initdir:?}/etc/systemd/system-generators/"
+    ln -s /dev/null "$initdir/etc/systemd/system-generators/systemd-rc-local-generator"
 }
 
 install_execs() {