Bump org.asciidoctor:asciidoctorj-diagram from 2.3.0 to 2.3.1 (#1723)

Bumps [org.asciidoctor:asciidoctorj-diagram](https://github.com/asciidoctor/asciidoctorj-diagram) from 2.3.0 to 2.3.1.
- [Release notes](https://github.com/asciidoctor/asciidoctorj-diagram/releases)
- [Commits](asciidoctor/asciidoctorj-diagram@v2.3.0...v2.3.1)

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

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

user_guides/parent/pom.xml

@@ -32,7 +32,7 @@
     <name>Eclipse Foundation Technology Compatibility Kit User's Guide Parent for TCK Documentation</name>
 
     <properties>
-        <asciidoctorj.diagram.version>2.3.0</asciidoctorj.diagram.version>
+        <asciidoctorj.diagram.version>2.3.1</asciidoctorj.diagram.version>
         <asciidoctorj.maven.plugin.version>3.1.0</asciidoctorj.maven.plugin.version>
         <asciidoctorj.pdf.version>2.3.19</asciidoctorj.pdf.version>