Update the shell scripts to always have a shebang and use whether bash:

#!/usr/bin/env bash

or the system shell:

#!/bin/sh

Other forms will throw an arcanist error at lint time.

Backport of core PR13320, PR13510 and PR14831
https://github.com/bitcoin/bitcoin/pull/13320/files
https://github.com/bitcoin/bitcoin/pull/13510/files
https://github.com/bitcoin/bitcoin/pull/14831/files

Depends on D3945.

Edit a shell script to have a bas shebang then run:

arc lint

Ensure the linter catches the error.

Should return no error (requires D3946 to have zero output):

arc lint --everything