Fix WebappLoader constructor deprecations

See gh-20832

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatReactiveWebServerFactory.java

@@ -149,7 +149,7 @@ public class TomcatReactiveWebServerFactory extends AbstractReactiveWebServerFac
 		context.addLifecycleListener(new Tomcat.FixContextListener());
 		context.setParentClassLoader(ClassUtils.getDefaultClassLoader());
 		skipAllTldScanning(context);
-		WebappLoader loader = new WebappLoader(context.getParentClassLoader());
+		WebappLoader loader = new WebappLoader();
 		loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());
 		loader.setDelegate(true);
 		context.setLoader(loader);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/tomcat/TomcatServletWebServerFactory.java

@@ -222,7 +222,7 @@ public class TomcatServletWebServerFactory extends AbstractServletWebServerFacto
 			// Tomcat is < 8.5.39. Continue.
 		}
 		configureTldSkipPatterns(context);
-		WebappLoader loader = new WebappLoader(context.getParentClassLoader());
+		WebappLoader loader = new WebappLoader();
 		loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());
 		loader.setDelegate(true);
 		context.setLoader(loader);