Bump struts2-core from 2.5.29 to 2.5.31 in /app

Bumps [struts2-core](https://github.com/apache/struts) from 2.5.29 to 2.5.31.
- [Release notes](https://github.com/apache/struts/releases)
- [Commits](https://github.com/apache/struts/commits)

---
updated-dependencies:
- dependency-name: org.apache.struts:struts2-core
  dependency-type: direct:production
...

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

Author: dependabot[bot]

app/pom.xml

@@ -57,7 +57,7 @@ limitations under the License.
         <slf4j.version>1.7.36</slf4j.version>
         <spring.version>5.3.25</spring.version>
         <spring.security.version>5.8.2</spring.security.version>
-        <struts.version>2.5.29</struts.version>
+        <struts.version>2.5.31</struts.version>
         <velocity.version>2.3</velocity.version>
         <webjars.version>1.6</webjars.version>
         <ws-commons-util.version>1.0.2</ws-commons-util.version>