Give Gitea workflow reruns unique diagnostic names

.gitea/workflows/build.yaml

@@ -14,12 +14,15 @@ jobs:
       CI_COMMIT: ${{ gitea.sha }}
       CI_REF: ${{ gitea.ref }}
       CI_RUN_ID: ${{ gitea.run_id }}
-      CI_RUN_ATTEMPT: ${{ gitea.run_attempt }}
     steps:
       - name: Check out pushed commit
         uses: https://github.com/actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
           persist-credentials: false
+      - name: Identify workflow attempt
+        # Gitea 1.25 does not populate gitea.run_attempt. Use a unique value for
+        # container names and diagnostic artifacts, including reruns of one SHA.
+        run: printf 'CI_RUN_ATTEMPT=%s\n' "$(date -u +%Y%m%d%H%M%S%N)" >> "$GITHUB_ENV"
       - name: Build and test both images
         run: timeout --signal=TERM --kill-after=60s 75m bash ci/verify.sh
       - name: Publish verified main images
@@ -35,7 +38,7 @@ jobs:
         if: always()
         uses: https://github.com/actions/upload-artifact@ff15f0306b3f739f7b6fd43fb5d26cd321bd4de5
         with:
-          name: diagnostics-${{ gitea.run_id }}-${{ gitea.run_attempt }}
+          name: diagnostics-${{ gitea.run_id }}-${{ env.CI_RUN_ATTEMPT }}
           path: ci/artifacts/
           if-no-files-found: error
           retention-days: 14