I am saying this as a former believer (and holding no grudge), definitely aware of the fine line between sharing and pushing cultural items, and balancing the two rather equally in a diverse team.
EDIT: actually, it's a topic in itself in a matter of company/team management. I saw a similar concern grow in one of my older team in a previous job, because the company "inclusion and diversity" department held a _very_ unbalanced and awkward take in this regard, talking a lot about some religious/cultural items, and ignoring quite a few others (from different equally present countries of origin and faiths), actually resulting in a fracture in the self-perceived image of the team. That's really a delicate matter.
The occasional celebratory post is fine on HN. If it were to become repetitive, it would get tedious quickly and we would downweight such posts in keeping with standard practice (see [1] and [2] about that).
[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
[2] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
If the only criteria for allowing posts like these is "People can wish each other well without coming close to that" then HN can easily be flooded with junk posts from every single Religious (and any other) group (Real/Imaginary and Bonkers) for every single day of the year.
If people start posting too many of them, we'll downweight them the same way we would any other repetitive pattern—not because we have any problem with their particular topic but because repetition quickly becomes tedious. (And users would flag them increasingly heavily in any case.)