fix o4b end date

https://observing.docs.ligo.org/plan/

LIGO, Virgo, and KAGRA have adopted a change to the end date for the O4 observing run, which previously had been set as February 2025. It has been decided to extend the O4 run, to allow for greater preparation of upgrade hardware that will be installed for O5. The new end date for O4 is 9 June 2025.