The people over at Blacksmith.sh have generously offered usage of their
runners for our organization, so let's try to switch over some simple
workflows. The runners should be drop-in replacements.
This action adds and removes the new "conflicts" label to indicate
whether a pull request is in need of conflict resolution. This both
automatically informs the author of the PR that this is the case, if
they have notifications enabled that is, and makes for an easier
evaluation of the PR queue.
