Bump org.openjdk.nashorn:nashorn-core from 15.4 to 15.6 (#1730)

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

examples/testing-security-4/pom.xml

@@ -73,7 +73,7 @@
     <dependency>
       <groupId>org.openjdk.nashorn</groupId>
       <artifactId>nashorn-core</artifactId>
-      <version>15.4</version>
+      <version>15.6</version>
       <scope>test</scope>
     </dependency>
     <!--

pom.xml

@@ -147,7 +147,7 @@
     <version.osgi.framework>4.2.0</version.osgi.framework>
     <version.aether>1.13.1</version.aether>
     <version.xalan>2.7.3</version.xalan>
-    <version.nashorn>15.4</version.nashorn>
+    <version.nashorn>15.6</version.nashorn>
 
     <!-- Logging frameworks -->
     <version.slf4j>2.0.16</version.slf4j>