Coding standards: use short array syntax

I'm planning to incorporate this ticket into 📌 Adopt GitLab CI template Needs review so we can fix all those things in one single merge request.

Updating issue credits, not giving credits for simply applying PHPCBF.

I can also confirm there are no more occurrences of "Drupal.Arrays.DisallowLongArraySyntax.Found" in the latest CI run: https://git.drupalcode.org/project/poll/-/jobs/714963

So the RTBC is justified.

Automatically closed - issue fixed for 2 weeks with no activity.