[FLINK-36595][docs] Explicitly set connector compatibility as string

Author: reswqa

docs/data/elastic.yml

@@ -17,7 +17,7 @@
 ################################################################################
 
 version: 4.0.0
-flink_compatibility: [2.0]
+flink_compatibility: ["2.0"]
 variants:
   - maven: flink-connector-elasticsearch6
     sql_url: https://repo.maven.apache.org/maven2/org/apache/flink/flink-sql-connector-elasticsearch6/$full_version/flink-sql-connector-elasticsearch6-$full_version.jar