Upgrade to Tomcat 9.0.31

Closes gh-20253

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -190,7 +190,7 @@
 		<thymeleaf-layout-dialect.version>2.3.0</thymeleaf-layout-dialect.version>
 		<thymeleaf-extras-data-attribute.version>2.0.1</thymeleaf-extras-data-attribute.version>
 		<thymeleaf-extras-java8time.version>3.0.4.RELEASE</thymeleaf-extras-java8time.version>
-		<tomcat.version>9.0.30</tomcat.version>
+		<tomcat.version>9.0.31</tomcat.version>
 		<unboundid-ldapsdk.version>4.0.14</unboundid-ldapsdk.version>
 		<undertow.version>2.0.29.Final</undertow.version>
 		<webjars-hal-browser.version>3325375</webjars-hal-browser.version>

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.
@@ -153,7 +153,9 @@ public 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())