scripts: Use portable paste invocation in language check

[simonjbeaumont]

Motivation

The script that checks for unacceptable language used an invocation of paste that worked on Linux (i.e. in the CI), but not with the variant of paste preinstalled on Darwin platforms.

This meant it failed like this:

❯ bash scripts/check-for-unacceptable-language.sh
** Checking for unacceptable language...
usage: paste [-s] [-d delimiters] file ...

Worse, the || true was in the wrong place so it failed silently.

Modifications

• Use portable invocation of paste for Linux and Darwin.
• Move the || true so that, when it fails, it fails hard.

Result

Can run the script on Darwin.

Testing

❯ bash scripts/check-for-unacceptable-language.sh
** Checking for unacceptable language...
** ✅ Found no unacceptable language.

❯ echo kill  >> README.md

❯ bash scripts/check-for-unacceptable-language.sh
** Checking for unacceptable language...
** ERROR: ❌ Found unacceptable language in files: README.md.