fix: retry version resolution

Jenkinsfile

@@ -99,11 +99,20 @@ spec:
                   echo "${HARBOR_VERSION}"
                   exit 0
                 fi
-                curl -sSL https://api.github.com/repos/goharbor/harbor/releases/latest | python3 - <<'PY'
-import json, sys
-data = json.load(sys.stdin)
-print(data.get("tag_name", "").strip())
-PY
+                for attempt in 1 2 3; do
+                  version=$(curl -fsSL \
+                    -H 'Accept: application/vnd.github+json' \
+                    -H 'User-Agent: harbor-arm-build' \
+                    https://api.github.com/repos/goharbor/harbor/releases/latest \
+                    | jq -r '.tag_name // empty') || version=""
+                  if [ -n "${version}" ]; then
+                    echo "${version}"
+                    exit 0
+                  fi
+                  sleep $((attempt * 5))
+                done
+                echo "Failed to resolve Harbor version from GitHub; set HARBOR_VERSION manually." >&2
+                exit 1
               '''
             ).trim()
             env.HARBOR_VERSION_RESOLVED = resolved