Polish code with code cleanup rules

spring-boot-project/spring-boot-tools/spring-boot-loader-classic/src/main/java/org/springframework/boot/loader/jar/StringSequence.java

@@ -76,6 +76,7 @@ final class StringSequence implements CharSequence {
 	 * Returns {@code true} if the sequence is empty. Public to be compatible with JDK 15.
 	 * @return {@code true} if {@link #length()} is {@code 0}, otherwise {@code false}
 	 */
+	@Override
 	public boolean isEmpty() {
 		return length() == 0;
 	}