Bump org.asciidoctor:asciidoctorj-pdf in /quarkus-workshop-super-heroes

Bumps [org.asciidoctor:asciidoctorj-pdf](https://github.com/asciidoctor/asciidoctorj-pdf) from 2.3.9 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](asciidoctor/asciidoctorj-pdf@v2.3.9...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]>

quarkus-workshop-super-heroes/docs/pom.xml

@@ -35,7 +35,7 @@ The default build will take around 50m.
         <version.asciidoctor.maven.plugin>2.2.4</version.asciidoctor.maven.plugin>
         <version.jruby>9.4.5.0</version.jruby>
         <version.asciidoctorj>2.5.10</version.asciidoctorj>
-        <version.asciidoctorj.pdf>2.3.9</version.asciidoctorj.pdf>
+        <version.asciidoctorj.pdf>2.3.18</version.asciidoctorj.pdf>
         <version.asciidoctorj.diagram>2.2.13</version.asciidoctorj.diagram>
         <!-- If building docs locally and urls matter, set environment variables for these values -->
         <github.raw>https://raw.githubusercontent.com/${env.GITHUB_REPOSITORY}/${env.GITHUB_REF}/quarkus-workshop-super-heroes</github.raw>