Pin upload-artifact to v3 for Gitea Actions compatibility

Gitea Actions runner does not support actions/upload-artifact v2.0.0+
(error: "@actions/artifact v2.0.0+, upload-artifact@v4+ and
download-artifact@v4+ are not currently supported on GHES").

The v4 release switched to a new artifact API that only GitHub-hosted
runners implement. v3 still uses the v1 API and works on Gitea /
self-hosted / GHES runners.

Downgraded in both sku-catalog-refresh.yaml and kb-health.yaml.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/kb-health.yaml

@@ -68,7 +68,7 @@ jobs:
 
       - name: Upload report
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: kb-health-report
           path: /tmp/link-check.txt

.gitea/workflows/sku-catalog-refresh.yaml

@@ -67,7 +67,7 @@ jobs:
 
       - name: Upload logs as artifact
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: sku-refresh-logs
           path: |