Fix javadoc for getJobNames() method

Clarify that the method returns job names (not job instances)
for all jobs that have at least one job instance in the repository.

Resolves FIXME comment about ambiguous javadoc description.

Signed-off-by: HJC96 <gkswlcjs2@naver.com>

(cherry picked from commit 69da1b7)

Author: HJC96

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JobInstanceDao.java

@@ -103,9 +103,9 @@ default JobInstance getLastJobInstance(String jobName) {
 	}
 
 	/**
-	 * Retrieve the names of all job instances sorted alphabetically - i.e. jobs that have
-	 * ever been executed.
-	 * @return the names of all job instances
+	 * Retrieve the names of all jobs for which job instances exist, sorted
+	 * alphabetically.
+	 * @return the names of all jobs with job instances
 	 */
 	List<String> getJobNames();