Add Sniff to enforce shorthand array syntax

[jaymcp]

Description

Fixes #176 - our array syntax standards were not being enforced.

Changelog

• Enforce shorthand array syntax

Types of changes (if applicable):

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Checklist (if applicable):

• All checks pass when running `composer run all-checks.