timezone related bug of git

Hi，

 I found a timezone related bug in the git:

1. git log 11990eba -1 --date=format:%s

commit 11990eba0be50d1ad0655ede4062b7130326c41f (HEAD -> trunk,
origin/trunk, origin/HEAD)
Author: rillig [off-list ref]
Date:   1635604878

    indent: move debugging functions to a separate section

2. git cat-file -p 11990eba

tree 5d62150f5e2bafd3db76641450ca5d902302a039
parent 892557a74bd49983fac28366b772b53c9216ca73
author rillig [off-list ref] 1635633678 +0000
committer rillig [off-list ref] 1635633678 +0000

indent: move debugging functions to a separate section

3. conclusion

The unix time stored in git repository not same as the git log output,
then there must be a timezone offset bug:

1635633678 - 1635604878 = 28800 = 8 hours (local timezone offset)

Best regards,
Cauchy Song