Upgrade to Tomcat 8.5.21

Closes gh-10395

spring-boot-dependencies/pom.xml

@@ -192,7 +192,7 @@
 		<thymeleaf-layout-dialect.version>2.2.2</thymeleaf-layout-dialect.version>
 		<thymeleaf-extras-data-attribute.version>2.0.1</thymeleaf-extras-data-attribute.version>
 		<thymeleaf-extras-java8time.version>3.0.1.RELEASE</thymeleaf-extras-java8time.version>
-		<tomcat.version>8.5.20</tomcat.version>
+		<tomcat.version>8.5.21</tomcat.version>
 		<undertow.version>1.4.20.Final</undertow.version>
 		<unboundid-ldapsdk.version>3.2.1</unboundid-ldapsdk.version>
 		<webjars-hal-browser.version>3325375</webjars-hal-browser.version>
@@ -1360,6 +1360,11 @@
 				<artifactId>tomcat-embed-websocket</artifactId>
 				<version>${tomcat.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.apache.tomcat</groupId>
+				<artifactId>tomcat-annotations-api</artifactId>
+				<version>${tomcat.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.apache.tomcat</groupId>
 				<artifactId>tomcat-jdbc</artifactId>