RuboCop: Enforce shorthand syntax for hash in Style/HashSyntax

What does this MR do and why?

Contributes to #435940 (closed).

See #435940 (comment 1703307479)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

✅

How to set up and validate locally

bundle exec rubocop --parallel --only Style/HashSyntax

for gemfile in $(ls gems/*/Gemfile); do (cd $(dirname $gemfile) && bundle && bundle exec rubocop); done