test-one-license: modernize bash script

[quantenzitrone]

this makes the script runnable on nixos and other distros that don't install bash in /bin

[xsuchy]

+1 to /usr/bin
but -1 to env because of https://jmmv.dev/2016/09/env-considered-harmful.html
Can you just put there /usr/bin/bash ?

[quantenzitrone]

changing /bin/bash to /usr/bin/bash doesn't make it any more portable.

e.g. on NixOS only /bin/sh and /usr/bin/env exist in their default locations.
everything else is installed in /run/current-system/sw/bin, ~/.local/state/nix/profile or sometimes even just part of the $PATH

or on MacOS /bin/bash is stuck on some old version because Apple couldn't handle GPL3 or something
using /usr/bin/env bash makes it possible to run the script with the homebrew installed bash in /opt/homebrew/bin/bash

I disagree with quite a few points in this blog post:
i-iii) using anything other than /usr/bin/env doesn't guarantee that the correct interpreter is used, however using /usr/bin/env lets the user set the correct interpreter using by configuring $PATH
v) The entire point of using /usr/bin/env is to be at the mercy of the users environment configuration.
Why is not ok for a program to assume $PATH contains the correct binary but it's ok for it to assume that the correct binary is installed in a specific location like /usr/bin/bash?

[xsuchy]

I still have my opinion about env, but if that resolves your problem on NixOS... it makes no harm on other OSes. So +1 from me.