When a PR is built, it is done using the merge of its code with the base branch (e.g. master). If there are several PRs opened and one of them is merged to master, the reasonable thing to do is to rebuild all the others to find out build errors/failed tests after the new merge with master.
Is there any way to do it? (BTW, the Jenkins plugin does exactly the same)
If not, is there a way to manually run an action from another action? This way I could write an action that on push to master goes over all the opened PRs and manually start the "CI" workflow.
@e-orz , currently, GitHub Actions does not support the features you requested, and also does not support to manually trigger workflow run.