fix: pin pygments<2.20 to fix MkDocs build

pymdown-extensions 10.21 passes filename=None to Pygments 2.20.0 HtmlFormatter,
causing 'NoneType' object has no attribute 'replace' error.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: HavenDV

.github/workflows/mkdocs.yml

@@ -39,7 +39,7 @@ jobs:
           dotnet-version: 10.0.x
 
       - name: Install dependencies
-        run: pip install mkdocs-material
+        run: pip install mkdocs-material 'pygments<2.20'
 
       - name: Install AutoSDK CLI
         run: dotnet tool install --global autosdk.cli --prerelease