Polish "Encourage use of maven-publish plugin in Gradle docs"

See gh-25299

Author: wilkinsona

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/asciidoc/publishing.adoc

@@ -25,6 +25,9 @@ include::../gradle/publishing/maven-publish.gradle.kts[tags=publishing]
 
 [[publishing-your-application-maven]]
 === Publishing with the Maven Plugin
+WARNING: The `maven` plugin has been deprecated in Gradle 6 and has been removed in Gradle 7.
+Please use the `maven-publish` plugin instead.
+
 When the {maven-plugin}[`maven` plugin] is applied, an `Upload` task for the `bootArchives` configuration named `uploadBootArchives` is automatically created.
 By default, the `bootArchives` configuration contains the archive produced by the `bootJar` or `bootWar` task.
 The `uploadBootArchives` task can be configured to publish the archive to a Maven repository:
@@ -41,7 +44,7 @@ include::../gradle/publishing/maven.gradle[tags=upload]
 include::../gradle/publishing/maven.gradle.kts[tags=upload]
 ----
 
-WARNING: The maven plugin has been deprecated in Gradle 6.0 and is scheduled to be removed in Gradle 7.0. Please use the maven-publish plugin instead.
+
 
 [[publishing-your-application-distribution]]
 === Distributing with the Application Plugin