update arbitrary config test flags for upload uniqueness

.github/workflows/build_and_test.yml

@@ -287,7 +287,7 @@ jobs:
     - uses: "./.github/actions/upload_coverage"
       if: always()
       with:
-        flags: ${{ env.pg_major }}_upgrade
+        flags: ${{ env.pg_major }}_arbitrary_configs_${{ matrix.parallel }}
         codecov_token: ${{ secrets.CODECOV_TOKEN }}
   test-pg-upgrade:
     name: PG${{ matrix.old_pg_major }}-PG${{ matrix.new_pg_major }} - check-pg-upgrade