`configuration.statuses.characters_reserved_per_url` missing from some Pleroma servers

Environment

• Pleroma version (could be found in the "Version" tab of settings in Pleroma-FE): "2.7.2 (compatible; Pleroma 2.6.51-650-g0b9bc4a0-develop)" (at least, but see below)

Bug description

I see a number of Plerorma servers that have somehow been configured such that characters_reserved_per_url is missing from the /api/v2/instance response.

That's a non-optional, non-nullable property according to https://docs.joinmastodon.org/entities/Instance/#characters_reserved_per_url, so should be present.

Affected servers include: activitypub.agates.io, apontaeclica.com, bassam.social, bearvideo.win, c.wtf, clew.lol, fediverse.spearman.xyz, foygl.com, gleasonator.com, hidamari.apartments, iddqd.social, idolheaven.org, jacksonhomestead.me, killyour.dad, leafposter.club, lm.kazv.moe, neenster.org, orwell.fun, p.sugar-free-jazz.com, parcero.bond, pl.eragon.re, pl.fediverse.pl, pl.kotobank.ch, pleroma.dark-alexandr.net, pleroma.pibvt.net, pleroma.woodynet.net, rabbithou.se, rebased.social, rebased.taihou.website, redsnake.io, seal.cafe, shinkai.party, shitposting.on.incorrigible.moe, social.dansonline.space, social.linuxine.net, social.luizpicolo.com.br, social.protectors.moe, social.rucksfuchs.de, social.teci.world, socialgoblins.club, sosial.agdersam.no, svltan.at, twhtv.club, updog.no, vnil.de, vocalfry.social

Many of those servers are in the list in 3249 as well, which is why I've linked the issues in case there's something in common between them.