Bump log4j2.version from 2.20.0 to 2.21.0

Bumps `log4j2.version` from 2.20.0 to 2.21.0.

Updates `org.apache.logging.log4j:log4j-core` from 2.20.0 to 2.21.0

Updates `org.apache.logging.log4j:log4j-api` from 2.20.0 to 2.21.0

Updates `org.apache.logging.log4j:log4j-slf4j-impl` from 2.20.0 to 2.21.0

---
updated-dependencies:
- dependency-name: org.apache.logging.log4j:log4j-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-api
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-slf4j-impl
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index c641241..ebca1f8 100644
--- a/pom.xml
+++ b/pom.xml
@@ -44,7 +44,7 @@
         <maven.compiler.source>11</maven.compiler.source>
         <maven.compiler.target>11</maven.compiler.target>
         <struts2.version>6.2.0</struts2.version>
-        <log4j2.version>2.20.0</log4j2.version>
+        <log4j2.version>2.21.0</log4j2.version>
         <jetty-plugin.version>11.0.15</jetty-plugin.version>
         <maven.javadoc.skip>true</maven.javadoc.skip>
         <jackson.version>2.14.1</jackson.version>