MFC: contrib/tzdata: import tzdata 2020f

Merge commit '96b88ac701b35ce68425046d4be8f51cb75b5d5b' into main

Changes: https://github.com/eggert/tz/blob/2020f/NEWS

(cherry picked from commit e35a01eec6926bfb5c088ca8961079b51a067bf3)
(cherry picked from commit ce87312019a18e6bd0c97c50e5762b38ffc21e76)

Approved by: so