[bot]: Bump org.asciidoctor:asciidoctorj-pdf from 2.3.7 to 2.3.18

Bumps [org.asciidoctor:asciidoctorj-pdf](https://github.com/asciidoctor/asciidoctorj-pdf) from 2.3.7 to 2.3.18.
- [Release notes](https://github.com/asciidoctor/asciidoctorj-pdf/releases)
- [Changelog](https://github.com/asciidoctor/asciidoctorj-pdf/blob/main/CHANGELOG.adoc)
- [Commits](https://github.com/asciidoctor/asciidoctorj-pdf/commits/v2.3.18)

---
updated-dependencies:
- dependency-name: org.asciidoctor:asciidoctorj-pdf
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

build/optaplanner-build-parent/pom.xml

@@ -465,7 +465,7 @@
               <!-- Required to generate the PDF file -->
               <groupId>org.asciidoctor</groupId>
               <artifactId>asciidoctorj-pdf</artifactId>
-              <version>2.3.7</version>
+              <version>2.3.18</version>
             </dependency>
           </dependencies>
         </plugin>