Upgrade timelib to 2021.06

Fixes among others:
. Bug #79580 (date_create_from_format misses leap year).
. Bug #80974 (Wrong diff between 2 dates in different timezones).
. Bug #8

Upgrade timelib to 2021.06

Fixes among others:
. Bug #79580 (date_create_from_format misses leap year).
. Bug #80974 (Wrong diff between 2 dates in different timezones).
. Bug #81097 (DateTimeZone silently falls back to UTC when providing an offset with seconds).
. Bug #81273 (Date interval calculation not correct).

show more ...