build: ensure PR repo and branch are checked out

Author: Planeshifter

.github/workflows/run_tests_coverage.yml

@@ -104,6 +104,12 @@ jobs:
 
           # Specify whether to download Git-LFS files:
           lfs: false
+
+          # Checkout PR branch if triggered by a pull request:
+          ref: ${{ github.event_name == 'pull_request_target' && github.event.pull_request.head.sha || '' }}
+
+          # Checkout PR repository (to properly work with forks) if triggered by a pull request:
+          repository: ${{ github.event_name == 'pull_request_target' && github.event.pull_request.head.repo.full_name || github.repository }}
         timeout-minutes: 10
 
       # Install Node.js: