Update ServerPropertiesTests to reflect updated default internalProxies

See gh-2699

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/ServerPropertiesTests.java

@@ -197,7 +197,10 @@ public class ServerPropertiesTests {
 		String expectedInternalProxies = "10\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|" // 10/8
 				+ "192\\.168\\.\\d{1,3}\\.\\d{1,3}|" // 192.168/16
 				+ "169\\.254\\.\\d{1,3}\\.\\d{1,3}|" // 169.254/16
-				+ "127\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}"; // 127/8
+				+ "127\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}|" // 127/8
+				+ "172\\.1[6-9]{1}\\.\\d{1,3}\\.\\d{1,3}|" // 172.16/12
+				+ "172\\.2[0-9]{1}\\.\\d{1,3}\\.\\d{1,3}|"
+				+ "172\\.3[0-1]{1}\\.\\d{1,3}\\.\\d{1,3}";
 
 		assertEquals(expectedInternalProxies, remoteIpValve.getInternalProxies());
 	}