CI: Add docutils test matrix (0.20, 0.21, 0.22)

Author: amotl

.github/workflows/main.yml

@@ -26,14 +26,30 @@ jobs:
           "3.9",
           "3.14",
         ]
+        docutils-version: [
+          "0.22.*",
+        ]
         sphinx-version: [
           "5.*",
           "6.*",
           "7.*",
           "8.*",
         ]
         exclude:
+
+          # Don't validate Sphinx 8 on Python 3.9.
           - python-version: "3.9"
+            docutils-version: "0.22.*"
+            sphinx-version: "8.*"
+
+        include:
+
+          # Validate on docutils 0.20 and 0.21.
+          - python-version: "3.14"
+            docutils-version: "0.20.*"
+            sphinx-version: "8.*"
+          - python-version: "3.14"
+            docutils-version: "0.21.*"
             sphinx-version: "8.*"
 
     env:
@@ -69,8 +85,9 @@ jobs:
         # Install package in editable mode.
         uv pip install --editable='.[develop,docs,test]'
 
-        # Install specific Sphinx version, according to test matrix slot.
+        # Install specific Sphinx and docutils versions, according to test matrix slots.
         uv pip install 'sphinx==${{ matrix.sphinx-version }}'
+        uv pip install 'docutils==${{ matrix.docutils-version }}'
 
         # Display Sphinx version.
         sphinx-build --version