Update master-pr-build.yml

Attempting to fix Github Action for incoming pull requests as per https://github.com/actions/first-interaction/issues/10#issuecomment-910605074
diff --git a/.github/workflows/master-pr-build.yml b/.github/workflows/master-pr-build.yml
index d51f9b3..fd641e9 100644
--- a/.github/workflows/master-pr-build.yml
+++ b/.github/workflows/master-pr-build.yml
@@ -18,7 +18,7 @@
 name: master pr build
 
 on:
-  pull_request:
+  pull_request_target:
     branches:
       - master
 
@@ -60,4 +60,4 @@
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           check_name: Test Report (${{ matrix.java }})
-          report_paths: '**/*-reports/TEST-*.xml'
\ No newline at end of file
+          report_paths: '**/*-reports/TEST-*.xml'