RHDH release date update

Keep release-schedule.yaml (GitHub) and release_calendar.yaml (GitLab CEE) in sync with the authoritative RHDH release schedule. Both files drive automation the plugin ecosystem already depends on: release-schedule.yaml feeds notify-3rd-party-owners.yaml's GitHub-issue reminders, and release_calendar.yaml feeds the rhdh-jira-lint bot's Slack posts to #forum-rhdh-releases and #rhdh-plugins-ecosystem. A stale date in either file produces a wrong reminder or a wrong Slack message with no review step — that is what this skill exists to prevent.

Scope

In scope: release-schedule.yaml and release_calendar.yaml — correcting stale entries and adding entries for newly-scheduled releases.

Out of scope, reported as a checklist item instead of fixed: