Bump junit from 4.12 to 4.13.1 in /samples/struts2/pet-store (#388)

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] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

samples/struts2/pet-store/pom.xml

@@ -28,7 +28,7 @@
         <maven.compiler.target>1.8</maven.compiler.target>
         <struts2.version>2.5.22</struts2.version>
         <jackson.version>2.10.3</jackson.version>
-        <junit.version>4.12</junit.version>
+        <junit.version>4.13.1</junit.version>
         <log4j.version>2.13.3</log4j.version>
     </properties>