docs: update issue template versions

Author: setchy

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -38,6 +38,7 @@ body:
       label: Gitify Version
       description: What version of Gitify are you using?
       options:
+        - 5.6.0
         - 5.5.0
         - 5.4.0
         - 5.3.0