release: generated tracking issue has incorrect dates when run from non-PST time zone

Created by: bobheadxi

I updated https://github.com/sourcegraph/sourcegraph/issues/14064 by running the tracking issue command and logging the body. However, it seems that the dates generated were incorrect (off by 1 day), which might have something to do with my time zone (GMT+8)

For consistency we probably want to choose a time zone to standardize on for this (probably PST) and have all release dates align with that time zone