Use /usr/bin/env in shebangs

configs/baseline/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e -u
 

configs/releng/airootfs/root/.automated_script.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 script_cmdline ()
 {

configs/releng/airootfs/root/customize_airootfs.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e -u
 

configs/releng/build.sh

-#!/bin/bash
+#!/usr/bin/env bash
 
 set -e -u