chart-diff: some diffs are hidden sometimes for branches pre chart model migration

[lucasrodes]

One-liner

After the recent migration to the chart_config table (see owid/owid-grapher#3767), some chart diffs are hidden in the app.

Context & details

Mojmir (from Slack):

It’s not easily fixable by code, but it’ll work if you re-save those charts in admin. (This will change their updatedAt timestamp and everything’s gonna work like before)

[Marigold]

For the context - I only saw this issue on one staging server, not sure if any other were affected. The problem was that function _get_staging_creation_time didn't return the correct time of server creation.

I haven't thoroughly investigated why. We use the creation time of charts table (with show table status like 'charts'), but it got changed on that server and charts that were updated before weren't showing up.

It's a one-time thing, it should be good after re-saving charts or with new staging servers.

[larsyencken]

From triage discussion, we think that you were the unlucky last person to experience it, and that it won't come up again for new work.