When a contributor opens their first pull request to `wordpress-develop`, the “Welcome” workflow runs and leaves a comment with guidance, helpful information, and resources.
However, because a workflow run triggered by the `pull_request` event runs against the workflow and code from the merge commit, the needed context and permissions to comment on the pull request are missing. By changing the trigger event to `pull_request_target`, the workflow runs against the workflow and code in the base of the pull request and is able to comment on when appropriate.
See #50401.
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git-svn-id: http://core.svn.wordpress.org/trunk@48931 1a063a9b-81f0-0310-95a4-ce76da25c4cd