Bump org.openjdk.nashorn:nashorn-core from 15.4 to 15.6

Bumps [org.openjdk.nashorn:nashorn-core](https://github.com/openjdk/nashorn) from 15.4 to 15.6.
- [Changelog](https://github.com/openjdk/nashorn/blob/main/CHANGELOG.md)
- [Commits](openjdk/nashorn@release-15.4...release-15.6)

---
updated-dependencies:
- dependency-name: org.openjdk.nashorn:nashorn-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

log4j-parent/pom.xml

@@ -125,7 +125,7 @@
     <log4j2-logstash-layout.version>0.18</log4j2-logstash-layout.version>
     <maven.version>3.9.9</maven.version>
     <mockito.version>5.14.2</mockito.version>
-    <nashorn.version>15.4</nashorn.version>
+    <nashorn.version>15.6</nashorn.version>
     <opentest4j.version>1.3.0</opentest4j.version>
     <org.eclipse.osgi.version>3.22.0</org.eclipse.osgi.version>
     <oro.version>2.0.8</oro.version>