fix: update shebangs to use bash from /usr/bin/env instead of /bin/ for better portability

[MrMebelMan]

Fixes #693

Proposed changes

As said in the issue, on some systems, bash doesn't lie in /bin/, but in other places, like /usr/local/bin/bash (FreeBSD) or even in unpredictable paths like /nix/store/y0vp7qcjz02rsgawlgmx8ilbh2wimcg5-system-path/bin/bash (NixOS).
It makes the installation impossible without modifying the Makefile.
This PR replaces all /bin/bash shebangs with /usr/bin/env bash, improving portability.

Checklist

• I have read the contributing guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security. vulnerability, I
  confirm that I got green light (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further comments

I consider /usr/bin env to be more portable, because env is more likely to be in /usr/bin than bash is to be in /bin.

[CLAassistant]

All committers have signed the CLA.

[MrMebelMan]

Lol, since the CI tests have failed, I suppose /usr/bin env is not as portable as I thought 😅

[aeneasr]

😅 the CI failed because of a different reason but if you run make format it should pass!

[aeneasr]

I think this is good to merge as is