stack/slapos.cfg: version up dateparser for py3

0.7.6 is the last version that support py2

but it has memory leak, which is only fixed at https://github.com/scrapinghub/dateparser/releases/tag/v1.1.8

let's upgrade version only for py3, to check if it fix the testGC when do import dateparser

we need to update to 1.2.1, pytz to 2025.2, also tzlocal to 5.3.1

otherwise some zodbtools tests failed