Update leap-seconds to leap-seconds.3676924800

Obtained from: ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.3676924800
Approved by: re (gjb)
(cherry picked from commit 1d333074349abb736ffdca9e6baf6c71aef4553b)
(cherry picked from commit 08038f3cbf197cc90b0ba89bb0e4d0e9cc287366)