process replay: don't upload if diff doesn't exist (#27333)

* fail the replay, successfully print

* should still run

* debug

* outside?

* don't fail

* don't fail

* don't fail

* test

* test

* test

* try this now

* clean up, works!

.github/workflows/selfdrive_tests.yaml

@@ -250,6 +250,7 @@ jobs:
         ${{ env.RUN }} "CI=1 coverage run selfdrive/test/process_replay/test_processes.py -j$(nproc) && \
                         coverage xml"
     - name: Print diff
+      id: print-diff
       if: always()
       run: cat selfdrive/test/process_replay/diff.txt
     - uses: actions/upload-artifact@v2
@@ -259,7 +260,7 @@ jobs:
         name: process_replay_diff.txt
         path: selfdrive/test/process_replay/diff.txt
     - name: Upload reference logs
-      if: ${{ failure() && github.event_name == 'pull_request' && github.repository == 'commaai/openpilot' && env.AZURE_TOKEN != '' }}
+      if: ${{ failure() && steps.print-diff.outcome == 'success' && github.event_name == 'pull_request' && github.repository == 'commaai/openpilot' && env.AZURE_TOKEN != '' }}
       run: |
         ${{ env.RUN }} "CI=1 AZURE_TOKEN='$AZURE_TOKEN' python selfdrive/test/process_replay/test_processes.py -j$(nproc) --upload-only"
     - name: "Upload coverage to Codecov"