github: Allow AsciiDoc content in tests to render Ditaa diagrams

In 2c80dee we enabled rendering of
PlantUML diagrams within integration tests. This commit removes PlantUML
support from the tests in favor of rendering Ditaa diagrams, which take
less time to generate.

Author: jmooring

.github/workflows/test.yml

@@ -52,8 +52,8 @@ jobs:
         run: |
           gem install asciidoctor -v "2.0.26"
           gem install asciidoctor-diagram -v "3.0.1"
-          gem install asciidoctor-diagram-plantuml -v "1.2025.3"
-      - name: Install Java # required by asciidoctor-diagram-plantuml
+          gem install asciidoctor-diagram-ditaamini -v "1.0.3"
+      - name: Install Java # required by asciidoctor-diagram-ditaamini
         uses: actions/setup-java@dded0888837ed1f317902acf8a20df0ad188d165 # v5.0.0
         with:
           distribution: temurin