Bump org.asciidoctor:asciidoctorj-pdf from 2.3.20 to 2.3.21 (#346)

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

Author: dependabot[bot]

pom.xml

@@ -17,7 +17,7 @@
         <asciidoctor.maven.plugin.version>3.2.0</asciidoctor.maven.plugin.version>
         <asciidoctorj.version>2.5.1</asciidoctorj.version>
         <asciidoctorj.diagram.version>3.0.1</asciidoctorj.diagram.version>
-        <asciidoctorj.pdf.version>2.3.20</asciidoctorj.pdf.version>
+        <asciidoctorj.pdf.version>2.3.21</asciidoctorj.pdf.version>
         <jetty-maven-plugin.version>11.0.26</jetty-maven-plugin.version>
         <plantuml.version>1.2025.4</plantuml.version>
     </properties>