Bump junit from 3.8.1 to 4.13.1 in /java/example_code/iam

Bumps [junit](https://github.com/junit-team/junit4) from 3.8.1 to 4.13.1.
- [Release notes](https://github.com/junit-team/junit4/releases)
- [Changelog](https://github.com/junit-team/junit4/blob/main/doc/ReleaseNotes4.13.1.md)
- [Commits](https://github.com/junit-team/junit4/commits/r4.13.1)

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

Author: dependabot[bot]

java/example_code/iam/pom.xml

@@ -30,7 +30,7 @@
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
-      <version>3.8.1</version>
+      <version>4.13.1</version>
       <scope>test</scope>
     </dependency>
   </dependencies>