Bump junit from 4.12 to 4.13.1 in /samples/servlet-echo

Bumps [junit](https://github.com/junit-team/junit4) from 4.12 to 4.13.1.
- [Release notes](https://github.com/junit-team/junit4/releases)
- [Changelog](https://github.com/junit-team/junit4/blob/main/doc/ReleaseNotes4.12.md)
- [Commits](junit-team/junit4@r4.12...r4.13.1)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

samples/servlet-echo/pom.xml

@@ -46,7 +46,7 @@
       <dependency>
           <groupId>junit</groupId>
           <artifactId>junit</artifactId>
-          <version>4.12</version>
+          <version>4.13.1</version>
           <scope>test</scope>
       </dependency>
       <dependency>