Build(deps): bump io.undertow:undertow-core in /frameworks/Java/undertow (#10603)

Bumps [io.undertow:undertow-core](https://github.com/undertow-io/undertow) from 2.3.20.Final to 2.3.21.Final.
- [Release notes](https://github.com/undertow-io/undertow/releases)
- [Commits](undertow-io/undertow@2.3.20.Final...2.3.21.Final)

---
updated-dependencies:
- dependency-name: io.undertow:undertow-core
  dependency-version: 2.3.21.Final
  dependency-type: direct:production
...

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frameworks/Java/undertow/pom.xml

@@ -20,7 +20,7 @@
     <maven-jar-plugin.version>3.2.2</maven-jar-plugin.version>
     <mustache.version>0.9.10</mustache.version>
     <postgresql.version>42.7.2</postgresql.version>
-    <undertow.version>2.3.20.Final</undertow.version>
+    <undertow.version>2.3.21.Final</undertow.version>
   </properties>
 
   <dependencies>