Upgrade to Tomcat 9.0.31

Closes gh-20167

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizerTests.java

@@ -26,6 +26,7 @@ import org.apache.catalina.valves.AccessLogValve;
 import org.apache.catalina.valves.ErrorReportValve;
 import org.apache.catalina.valves.RemoteIpValve;
 import org.apache.coyote.AbstractProtocol;
+import org.apache.coyote.ajp.AbstractAjpProtocol;
 import org.apache.coyote.http11.AbstractHttp11Protocol;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -490,6 +491,8 @@ class TomcatWebServerFactoryCustomizerTests {
 	void ajpConnectorCanBeCustomized() {
 		TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory(0);
 		factory.setProtocol("AJP/1.3");
+		factory.addConnectorCustomizers(
+				(connector) -> ((AbstractAjpProtocol<?>) connector.getProtocolHandler()).setSecretRequired(false));
 		this.customizer.customize(factory);
 		WebServer server = factory.getWebServer();
 		server.start();

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -1765,7 +1765,7 @@ bom {
 			]
 		}
 	}
-	library("Tomcat", "9.0.30") {
+	library("Tomcat", "9.0.31") {
 		group("org.apache.tomcat") {
 			modules = [
 				"tomcat-annotations-api",

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/tomcat/SslConnectorCustomizerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -152,7 +152,9 @@ class SslConnectorCustomizerTests {
 		customizer.customize(connector);
 		this.tomcat.start();
 		SSLHostConfig sslHostConfig = connector.getProtocolHandler().findSslHostConfigs()[0];
+		sslHostConfig.getCertificates(true);
 		SSLHostConfig sslHostConfigWithDefaults = new SSLHostConfig();
+		sslHostConfigWithDefaults.getCertificates(true);
 		assertThat(sslHostConfig.getTruststoreFile())
 				.isEqualTo(SslStoreProviderUrlStreamHandlerFactory.TRUST_STORE_URL);
 		assertThat(sslHostConfig.getCertificateKeystoreFile())