set PULL in proper workflow file

.github/workflows/build-boards.yml

@@ -72,6 +72,7 @@ jobs:
       working-directory: tools
       env:
         BOARDS: ${{ matrix.board }}
+        PULL: ${{ github.event.number }}
 
     - name: Upload artifact
       uses: actions/upload-artifact@v3

.github/workflows/build.yml

@@ -84,7 +84,6 @@ jobs:
       run: python3 -u ci_set_matrix.py
       working-directory: tools
       env:
-        PULL: ${{ github.event.number }}
         LAST_FAILED_JOBS: ${{ steps.get-last-commit-with-checks.outputs.check_runs }}
 
   tests:
@@ -295,5 +294,3 @@ jobs:
     with:
       boards: ${{ toJSON(fromJSON(needs.scheduler.outputs.ports)[matrix.port]) }}
       cp-version: ${{ needs.scheduler.outputs.cp-version }}
-    env:
-      PULL: ${{ github.event.number }}