Case C-613/20: Judgment of the Court (Ninth Chamber) of 6 October 2021 (request for a preliminary ruling from the Landesgericht Salzburg — Austria) — CS v Eurowings GmbH (Reference for a preliminary ruling — Air transport — Regulation (EC) No 261/2004 — Article 5(3) — Common rules on compensation and assistance to passengers in the event of cancellation or long delay of flights — Exemption from the obligation to pay compensation — Concept of ‘extraordinary circumstances’ — Strike by airline staff — Strike by the staff of a subsidiary in solidarity with the staff of the parent company)