Support `workflow_run` events

[apexskier]

I'm attempting to use this workflow after being triggered by workflow_run, as described in https://securitylab.github.com/research/github-actions-preventing-pwn-requests/.

However, I get the error invalid event type: workflow_run (from here).

You can see how I'm using this at https://github.com/apexskier/nova-json-language-server/blob/ea98f31ada6c0a0561bfbee45dc92c2bc621687b/.github/workflows/dependencies.yml.

From what I see in the code, workflow_run could be supported by checking github.event.workflow_run.event and delegating to some of the other executors.

[apexskier]

Just found #144. It looks like the PR that resolved it was for workflow_dispatch, not workflow_run.

[pascalgn]

Thanks for the PR, it's merged now! 👍