Use `/usr/bin/env` to find bash

[abhillman]

Before submitting your pull request

• [x] I agree to license my code under the MPL 2.0 license.
• [x] I rebased my work on top of the main branch.
• [x] I ran npm test and all tests passed.
• [x] I added test coverages if relevant.

Description

This enables npm test to successfully call scripts in bin/ with the bash binary specified by PROFILE.

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Additional information:

In addition to potentially preferring an alternative version of bash than the one in /bin/bash, some distributions forego storing bash in bin/ at all, such as NixOS:

$ cat /etc/os-release | rg '^NAME=' -r ''
NixOS
$ which bash
/run/current-system/sw/bin/bash

Type of change

Select all that apply.

• [x] Bug fix
• [ ] New feature
• [ ] Major change (fix or feature that would cause existing functionality to work differently than in the current version)

Tag issues related to this pull request:

• n/a

Related pull requests:

• https://github.com/mozilla/multi-account-containers/commit/83687f63246e93400cc52d1cd6b854c949d40a3b

[dannycolin]

Definitely agree with the portability argument so LGTM. Thanks for your contribution :).