ci: run required checks to merge pr on prs as well

[clintonsteiner]

@akaihola this should fix the problem preventing #773 from being able to merge

[clintonsteiner]

nvm looks like there are mypy issues

[akaihola]

nvm looks like there are mypy issues

Yes, the error is

Run wearerequired/lint-action@v2.3.0
Error: This action does not have permission to create annotations on forks.
You may want to run it only on pull_request_target events with checks permissions set to write.
See https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#permissions for details.

So next step is to check why wearerequired/lint-action might fail with missing permissions, and either fix that or switch to a different way of running mypy and producing annotations (e.g. the GitHub annotations output plugin upcoming in Graylint 2.1.0, see akaihola/graylint#74).

[akaihola]

This error from build #677 I don't understand. Where does the branch name 816/merge come from?

Collecting darker@ git+https://github.com/akaihola/darker@816/merge
(from darker[black,color,isort]@ git+https://github.com/akaihola/darker@816/merge)
  Cloning https://github.com/akaihola/darker (to revision 816/merge) to /tmp/pip-install-83w0_ho0/darker_e8e2e482abc0429fb03aea40a872f477
  Running command git clone --filter=blob:none --quiet https://github.com/akaihola/darker \
                   /tmp/pip-install-83w0_ho0/darker_e8e2e482abc0429fb03aea40a872f477
  WARNING: Did not find branch or tag '816/merge', assuming revision or ref.
  Running command git checkout -q 816/merge
  error: pathspec '816/merge' did not match any file(s) known to git
  error: subprocess-exited-with-error
  
  × git checkout -q 816/merge did not run successfully.