Add note regarding aggregated Javadoc toolchain configuration

In commit 49ef150c5d, I stated that the common javadoc task used by all
spring-* modules would be addressed in a separate commit. However,
after further investigation I determined that the spring-test Javadoc
JAR was published successfully, including links to JUnit 5 Javadoc
(which was not previously the case).

https://repo1.maven.org/maven2/org/springframework/spring-test/7.0.0-M4/spring-test-7.0.0-M4-javadoc.jar

This commit therefore only adds a note in JavaConventions to remind us
that the aggregated Javadoc toolchain configuration needs to stay in
sync with the configuration in JavaConventions.

See gh-27497
Closes gh-34774

buildSrc/src/main/java/org/springframework/build/JavaConventions.java

@@ -42,12 +42,15 @@ public class JavaConventions {
 	private static final List<String> TEST_COMPILER_ARGS;
 
 	/**
-	 * The Java version we should use as the JVM baseline for building the project
+	 * The Java version we should use as the JVM baseline for building the project.
+	 * <p>NOTE: If you update this value, you should also update the value used in
+	 * the {@code javadoc} task in {@code framework-api.gradle}.
 	 */
 	private static final JavaLanguageVersion DEFAULT_LANGUAGE_VERSION = JavaLanguageVersion.of(24);
 
 	/**
-	 * The Java version we should use as the baseline for the compiled bytecode (the "-release" compiler argument)
+	 * The Java version we should use as the baseline for the compiled bytecode
+	 * (the "-release" compiler argument).
 	 */
 	private static final JavaLanguageVersion DEFAULT_RELEASE_VERSION = JavaLanguageVersion.of(17);