Code duplication: Update jscpd.yml to run in repo context (prebid#11757)

* Code duplication: Update jscpd.yml to run in repo context

* Update jscpd.yml

.github/workflows/jscpd.yml

@@ -1,7 +1,7 @@
 name: Check for Duplicated Code
 
 on: 
-  pull_request:
+  pull_request_target:
     branches:
       - master
 
@@ -40,8 +40,13 @@ jobs:
     - name: Run jscpd on entire codebase
       run: jscpd
 
+    - name: Fetch base and target branches
+      run: |
+        git fetch origin +refs/heads/${{ github.event.pull_request.base.ref }}:refs/remotes/origin/${{ github.event.pull_request.base.ref }}
+        git fetch origin +refs/pull/${{ github.event.pull_request.number }}/merge:refs/remotes/pull/${{ github.event.pull_request.number }}/merge
+
     - name: Get the diff
-      run: git diff origin/master...HEAD --name-only > changed_files.txt
+      run: git diff --name-only origin/${{ github.event.pull_request.base.ref }}...refs/remotes/pull/${{ github.event.pull_request.number }}/merge > changed_files.txt
 
     - name: List generated files (debug)
       run: ls -l