Update leap-seconds to latest leap-seconds.3676924800 (expires 2023-12-28)

Approved by: re (cperciva)
Obtained from: ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.3676924800
MFC after: 3 days

(cherry picked from commit df2fbbfa71b8ecc9e9e75ce85a635aade9c691cb)
(cherry picked from commit 0196b0944430916d5aaf0bb87571626b391c3138)