[FLINK-36189] Skip NPM build during Javadocs generation

(cherry picked from commit e8ca6be)

.github/workflows/docs.sh

@@ -53,6 +53,7 @@ mvn clean install -B -DskipTests -Dfast -Pskip-webui-build
 # build java/scala docs
 mkdir -p docs/target/api
 mvn javadoc:aggregate -B \
+    -Pskip-webui-build
     -Dmaven.javadoc.failOnError=true \
     -Dcheckstyle.skip=true \
     -Dspotless.check.skip=true \