Fix unwrapping of captured PrintStream in test support's OutputCapture

See gh-22214

Author: XenoAmess

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/system/OutputCapture.java

@@ -194,7 +194,7 @@ PrintStream getParent() {
 
 		private static PrintStream getSystemStream(PrintStream printStream) {
 			while (printStream instanceof PrintStreamCapture) {
-				return ((PrintStreamCapture) printStream).getParent();
+				printStream = ((PrintStreamCapture) printStream).getParent();
 			}
 			return printStream;
 		}