Bump io.undertow:undertow-servlet from 2.3.18.Final to 2.3.20.Final

Bumps [io.undertow:undertow-servlet](https://github.com/undertow-io/undertow) from 2.3.18.Final to 2.3.20.Final.
- [Release notes](https://github.com/undertow-io/undertow/releases)
- [Commits](undertow-io/undertow@2.3.18.Final...2.3.20.Final)

---
updated-dependencies:
- dependency-name: io.undertow:undertow-servlet
  dependency-version: 2.3.20.Final
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

environments/servlet/pom.xml

@@ -28,7 +28,7 @@
         <tomcat.version>11.0.11</tomcat.version>
         <jetty.version>12.1.1</jetty.version>
         <websockets.api>2.2.0</websockets.api>
-        <undertow.version>2.3.18.Final</undertow.version>
+        <undertow.version>2.3.20.Final</undertow.version>
     </properties>
 
     <!-- Import the BOMs -->