MFH: r481073

mail/thunderbird: update to 60.2.1 (rc1)

Release Notes: https://www.thunderbird.net/en-US/thunderbird/60.2.1/releasenotes/ (once ready)

PR: 231868
Approved by: maintainer (jbeich, gecko)
Security: c96d416a-eae7-4d5d-bc84-40deca9329fb

Approved by: portmgr (blanket: web browsers and the like)