[maven-release-plugin] prepare branch 15.0.x

Author: semaphore-agent-production[bot]

pom.xml

@@ -33,7 +33,7 @@
         <connection>scm:git:git://github.com/confluentinc/kafka-connect-elasticsearch.git</connection>
         <developerConnection>scm:git:git@github.com:confluentinc/kafka-connect-elasticsearch.git</developerConnection>
         <url>https://github.com/confluentinc/kafka-connect-elasticsearch</url>
-        <tag>HEAD</tag>
+        <tag>15.0.x</tag>
     </scm>
 
     <properties>