Fix infinite loop in FieldValues

Update `FieldValues` test object so that it doesn't cause an infinite
loop if it is actually created.

See gh-22040

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/fieldvalues/FieldValues.java

@@ -108,7 +108,7 @@ public class FieldValues {
 
 	private Integer[] integerArray = new Integer[] { 42, 24 };
 
-	private FieldValues[] unknownArray = new FieldValues[] { new FieldValues() };
+	private FieldValues[] unknownArray;
 
 	private Duration durationNone;