Do not rely on findAvailableTcpPort finding an available port

Closes gh-12779

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServer.java

@@ -266,7 +266,10 @@ public class UndertowServletWebServer implements WebServer {
 		List<Port> ports = new ArrayList<>();
 		for (Object listener : extractListeners()) {
 			try {
-				ports.add(getPortFromListener(listener));
+				Port port = getPortFromListener(listener);
+				if (port.getNumber() != 0) {
+					ports.add(port);
+				}
 			}
 			catch (Exception ex) {
 				// Continue

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/servlet/server/AbstractServletWebServerFactoryTests.java

@@ -933,7 +933,6 @@ public abstract class AbstractServletWebServerFactoryTests {
 		doWithBlockedPort((port) -> {
 			try {
 				AbstractServletWebServerFactory factory = getFactory();
-				factory.setPort(SocketUtils.findAvailableTcpPort(40000));
 				addConnector(port, factory);
 				AbstractServletWebServerFactoryTests.this.webServer = factory
 						.getWebServer();