Update all apps submodules to latest revisions

[jeromedalbert]

I was recently doing some "spring cleaning" by reviewing the freshness and pertinence of all the projects in apps/. So I thought I'd make this update PR to get the latest of everything. I have omitted some repos that have been deleted or moved: cf my other recent PRs for this.

It looks like dependabot does some updates on this repo, but I am still seeing a lot of revisions linked to commits from up to a year ago, even for important often-updated apps like dev.to, gitlab-hq and discourse. I guess it only does a few updates at a time maximum.