update year

[tasks] do return raw data when migrating old tasks

[.github] update workflow file

[repo] update legacy links

[deploy] remove importlib backport

[setup] temporarily restrict to requests<2.2.29

[frontend/submission_manager] catch DocumentTooLarge exception

Fixes #697.

This is a first mitigation and in all case useful, as the limit is set on the
total command sent to the MongoDB server, which cannot be computed before.

[course_admin] filter non activate and "empty username" users. (#919)

[frontend/tasks] fix call for task_user_can_submit

[backend] BackendJobDone should be sent to the job initiating client

Otherwise in database-shared multi-client (multiprocess) setup, another
client can kill a job it does not own and receive a JobDone it cannot process.