I'm used to the GNOME's GitLab workflow with merge requests, which means one can create wip branches and assign them to merge requests in the web UI, instead of creating a fork and cloning the whole repository to a new location. One is able to delete such branch as well.

The pagure interface suggests it can be done too, thus I did that, but a) I cannot rebase the branch (git rebase -i master && git push --atomic --force-with-lease); b) I cannot delete the wip branch.

I'd like to ask you to delete the branch for me.

It's this one:
https://src.fedoraproject.org/rpms/libsoup/tree/wip/mcrha/doc-subpackage

and some little info about it can be found in the associated pull request:
https://src.fedoraproject.org/rpms/libsoup/pull-request/1

I did find https://fedoraproject.org/wiki/Remove_dist-git_branches , which seems to be moved to https://docs.pagure.org/releng/sop_remote_dist_git_branches.html , but I cannot finish the very first step there:

$ ssh mcrha@pkgs.fedoraproject.org
PTY allocation request failed on channel 0
Welcome mcrha. This server does not offer shell access.
Connection to pkgs.fedoraproject.org closed.

Thus I cannot "self-service" this.