fix(jira): Make prefix check on "jira branch" command case-insensitive (#8799)

* Make prefix check on "jira branch" command case-insensitive

* Update plugins/jira/jira.plugin.zsh

Co-authored-by: Marc Cornellà <hello@mcornella.com>

* Fixing tabs to spaces

Co-authored-by: Robby Russell <robby@planetargon.com>
Co-authored-by: Marc Cornellà <hello@mcornella.com>