Extend the Fixes validation pattern to also accept JIRA issue references
(format: [A-Z]+-\d+) in addition to GitHub issue references. This allows
backport PRs to reference JIRA issues in the format 'Fixes: PROJECT-123'.
Fixes: https://github.com/scylladb/scylladb/issues/27571
Closes scylladb/scylladb#27572
(cherry picked from commit 3dfa5ebd7f)
Closes scylladb/scylladb#27599