Use array format for branch name

[joelostblom]

My editor detects the current syntax as incorrect. It seems like GitHub's docs also use the array format for single branch names, e.g. https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#using-activity-types-and-filters-with-multiple-events

[cderv]

I think the current syntax still works, but indeed preferred syntax is an array using [main] or - syntax;

Thanks !