avoid dup artifact saving and fail fast if it does not upload

.github/workflows/tests.yml

@@ -304,14 +304,16 @@ jobs:
           SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
       # part about saving PR number and then using it from auto-merge-dependabot-prs from:
       # https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#workflow_run
-      - name: Save PR number
+      - name: Write PR number to spiffworkflow-backend/pr dir
         if: ${{ github.event_name == 'pull_request' }}
         env:
           PR_NUMBER: ${{ github.event.number }}
         run: |
           mkdir -p ./pr
           echo "$PR_NUMBER" > ./pr/pr_number
-      - uses: actions/upload-artifact@v3
+      - name: Upload PR number as artifact
+        uses: actions/upload-artifact@v3
+        if: ${{ github.event_name == 'pull_request' }}
         with:
           name: pr_number
           # at https://github.com/sartography/spiff-arena/actions/runs/7757308061/job/21156982087, for example,
@@ -319,6 +321,7 @@ jobs:
           # from spiff-arena root rather than the default working-directory we specified, and therefore
           # trying to explicitly add spiffworkflow-backend to path
           path: spiffworkflow-backend/pr/
+          if-no-files-found: error
 
   tests-frontend:
     runs-on: ubuntu-latest
@@ -355,19 +358,6 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
-      # part about saving PR number and then using it from auto-merge-dependabot-prs from:
-      # https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#workflow_run
-      - name: Save PR number
-        if: ${{ github.event_name == 'pull_request' }}
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          mkdir -p ./pr
-          echo "$PR_NUMBER" > ./pr/pr_number
-      - uses: actions/upload-artifact@v3
-        with:
-          name: pr_number
-          path: pr/
 
   cypress-run:
     runs-on: ubuntu-latest