Although very common, bash is not guaranteed to be located at
`/bin/bash`. NixOS is an example of this.
More commonly, `/bin/bash` can be quite out of date. An example of this
is MacOS's version of `bash`. This realistically won't affect Playwright
but it's worth noting. You can technically update MacOS's system version
of bash but you need elevated permissions to do so.
By using `/usr/bin/env bash` instead of `/bin/bash` we can execute
Playwright's bash scripts in like NixOS and generally improve the
selection behaviour for bash in other systems too.
Some discussion of why it's worth favouring `/usr/bin/env bash` over
`/bin/bash`:
- Discusses `/bin/bash` missing in NixOS:
https://discourse.nixos.org/t/add-bin-bash-to-avoid-unnecessary-pain/5673
- Some general commentary on why `/usr/bin/env bash` is favoured:
https://askubuntu.com/a/1402721
- Points out how old bash is in MacOS:
https://itnext.io/upgrading-bash-on-macos-7138bd1066ba
Improves situation at #5501
