Upgrade the version of plantuml (#3124)

- directly use the official binaries instead of the ubuntu package
- upgrade the readthedocs ubuntu image to 22.04

.readthedocs.yml

@@ -4,10 +4,12 @@
 version: 2
 
 build:
-  os: "ubuntu-20.04"
+  os: "ubuntu-22.04"
   apt_packages:
+  - curl
+  - graphviz
   - npm
-  - plantuml
+  - openjdk-21-jre-headless
   - texlive
   tools:
     nodejs: "16"
@@ -16,6 +18,8 @@ build:
     post_install:
     - npm install -g [email protected]
     - npm install -g @mermaid-js/[email protected]
+    # If you change the `/tmp/plantuml.jar` path, be sure to also update where this path is used as well (e.g. in `conf.py`).
+    - curl -fsSL https://github.com/plantuml/plantuml/releases/download/v1.2024.3/plantuml-gplv2-1.2024.3.jar -o /tmp/plantuml.jar
 
 # Set requirements to build the docs
 python:

src/conf.py

@@ -112,7 +112,7 @@
     'sphinxcontrib.programoutput'
 ]
 
-plantuml = "/usr/bin/plantuml"
+plantuml = "/usr/bin/java -Djava.awt.headless=true -jar /tmp/plantuml.jar"
 plantuml_output_format = "svg_img"
 
 plot_html_show_source_link = True