Bump org.asciidoctor:asciidoctorj-pdf from 2.3.20 to 2.3.21

Bumps [org.asciidoctor:asciidoctorj-pdf](https://github.com/asciidoctor/asciidoctorj-pdf) from 2.3.20 to 2.3.21.
- [Release notes](https://github.com/asciidoctor/asciidoctorj-pdf/releases)
- [Changelog](https://github.com/asciidoctor/asciidoctorj-pdf/blob/main/CHANGELOG.adoc)
- [Commits](asciidoctor/asciidoctorj-pdf@v2.3.20...v2.3.21)

---
updated-dependencies:
- dependency-name: org.asciidoctor:asciidoctorj-pdf
  dependency-version: 2.3.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

pom.xml

@@ -30,7 +30,7 @@
         <maven-gpg-plugin.version>3.2.8</maven-gpg-plugin.version>
         <exec-maven-plugin.version>3.0.0</exec-maven-plugin.version>
         <maven-asciidoctor-plugin.version>3.2.0</maven-asciidoctor-plugin.version>
-        <asciidoctorj-pdf.version>2.3.20</asciidoctorj-pdf.version>
+        <asciidoctorj-pdf.version>2.3.21</asciidoctorj-pdf.version>
         <maven-site.version>3.21.0</maven-site.version>
         <maven-project-info-reports.version>3.9.0</maven-project-info-reports.version>
         <maven-javadoc-plugin.version>3.12.0</maven-javadoc-plugin.version>