ci: skip upload step when api key is empty (usually happens for PR)

scripts/upload-packages.sh

@@ -4,6 +4,11 @@ set -ex
 
 cd "$(git rev-parse --show-toplevel)"
 
+if [ -z "$GITEA_API_KEY" ]; then
+  echo "GITEA_API_KEY is empty, skip upload."
+  exit 0
+fi
+
 URL_BASE="$DRONE_GITEA_SERVER/api/packages/${DRONE_REPO_NAMESPACE}/generic/${DRONE_REPO_NAME}-build"
 
 for ZIP_NAME in *.zip; do