verify runs-on variable expansion happens on scheduled workflows
* Adds the TEST_SCHEDULE_RUNSON=docker variable
* Use it in a scheduled job
* Run this test only with Forgejo versions greater or equal to 8.0
otherwise it is not implemented yet
* replace the high level test running actions tests with end-to-end.sh
* set DOMAIN to the IP instead of 127.0.0.1 for runner <-> forgejo communications
* move forgejo_cli from a function to a file so that it can be used by forgejo-runner.sh
* keep the documentation updates workflows separate because they need to open one PR per version