Dart CI crashes

[provokateurin]

Since a few days almost all Dart CI jobs crash.
I believe this is related to either storage or memory limits (e.g. https://github.com/nextcloud/neon/actions/runs/13647643553/job/38149349606).
It's probably caused by the update to 31, because we now have even more docker images.
We could at least try to clean the build cache and remove any unused docker data, but as seen in the job run above it also already happens when building the docker images.

[provokateurin]

Removing support for 28 won't do that much unfortunately:

modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/cookbook/0.11
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/drop_account/2.4
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/drop_account/2.5
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/drop_account/2.6
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/drop_account/2.7
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/news/25.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/news/25.1
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/news/25.2
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/news/25.3
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/notes/4.10
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/notes/4.11
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/notes/4.8
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/notes/4.9
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/server/28.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/server/29.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/server/30.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/server/31.0
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/spreed/18.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/spreed/19.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/spreed/20.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/spreed/20.1
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/spreed/21.0
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/tables/0.6
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/tables/0.7
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/tables/0.8
modified:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/tables/0.9
new file:   packages/nextcloud/packages/nextcloud_test_presets/docker/presets/uppush/2.3

In theory spreed presets could be merged into the server presets, because they follow the same stable branches, except for 20.1 but I'm not sure how much 20.0 and 20.1 really differ.

Also removing 29 support (which is EOL next month) six more presets are going to get removed:

deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/drop_account/2.5
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/notes/4.9
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/server/29.0
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/spreed/19.0
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/tables/0.6
deleted:    packages/nextcloud/packages/nextcloud_test_presets/docker/presets/uppush/1.4

This will also then unblock #2379.

[provokateurin]

We could also limit the number of presets drastically by only testing against the latest app version for each server release.
Then we would only have four presets at the moment.
While not guaranteeing that everything works on all app versions, it's still quite ok and we already skip patch versions of apps since there would be too many.

[provokateurin]

Indeed, getting rid of a few presets makes the CI pass as expected: #2846
I'll also try if just dropping 28 is already enough for now, as that has been EOL since December and can be removed safely (and we already have a breaking change due to 31 support).

[provokateurin]

Removing the 28 presets was enough to make it work again.