fix: skip rotation issue actions when sprint has not advanced

[ppawlowski]

Description

This pull request fixes the recurring sprint rotation workflow misbehaving after the switch to 2-week sprints. The reusable workflow runs weekly, but previously always opened a next-sprint issue and closed the current one on every run — so during a mid-sprint week (when the sprint had not actually advanced) it created and closed rotation issues incorrectly.

A new check-sprint job now resolves the sprint active today and the one active at the next weekly run (today + 7d). If they are the same iteration, the sprint has not advanced and its continue output is false, gating out both the open-issue and close-previous-issue jobs.

Related Issue(s)

Closes FlowFuse/engineering#198

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes `flowforge.yml`?
  • Issue/PR raised on `FlowFuse/helm` to update ConfigMap Template
  • Issue/PR raised on `FlowFuse/CloudProject` to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the `area:migration` label