Make Asciidoctor tasks run when Java examples are updated

Closes gh-25892

buildSrc/src/main/java/org/springframework/boot/build/AsciidoctorConventions.java

@@ -128,6 +128,7 @@ class AsciidoctorConventions {
 		syncDocumentationSource.setDestinationDir(syncedSource);
 		syncDocumentationSource.from("src/docs/");
 		asciidoctorTask.dependsOn(syncDocumentationSource);
+		asciidoctorTask.getInputs().dir(syncedSource);
 		asciidoctorTask.setSourceDir(project.relativePath(new File(syncedSource, "asciidoc/")));
 		return syncDocumentationSource;
 	}