Fix timezone issue in SOURCE_DATE_EPOCH code

[kpcyrd]

This was flagged by an Arch Linux rebuilder:

│ │  ! file is build with mk_isdnhwdb
│ │  ! Do not change this file !!!
│ │  $01 258
│ │ -$02 Mon Jul  5 15:41:55 2021
│ │ +$02 Mon Jul  5 13:41:55 2021
│ │  ! name data
│ │  $03 5465
│ │  $05 Billion
│ │  $05 B009
│ │  $05 Billion B009
│ │  $05 ISDN Single Basic Rate
│ │  $05 PCI

Thanks!

cc: @bmwiedemann