Address @penghuo: revert stray blank line in doctest/build.gradle

After 'apply plugin: opensearch.testclusters', one blank line is enough
— restoring the single-blank spacing to match upstream/main.

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

doctest/build.gradle

@@ -15,7 +15,6 @@ plugins {
 
 apply plugin: 'opensearch.testclusters'
 
-
 def path = project(':').projectDir
 // temporary fix, because currently we are under migration to new architecture. Need to run ./gradlew run from
 // plugin module, and will only build ppl in it.