Use pull_request_target in PR project assignment.

Closes spring-projects#520

Author: mp911de

.github/workflows/project.yml

@@ -7,7 +7,7 @@ on:
  types: [opened, edited, reopened]
  issue_comment:
  types: [created]
- pull_request:
+ pull_request_target:
  types: [opened, edited, reopened]
 
 jobs: