to avoid AttributeError: 'NoneType' object has no attribute 'replace'

see github issue here: pygments/pygments#3076

Author: fracpete

.github/workflows/main.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install mkdocs==1.4.2 jinja2==3.1.2 "Markdown<3.4.0" mkdocs-material==8.5.10
+          pip install mkdocs==1.4.2 jinja2==3.1.2 "Markdown<3.4.0" mkdocs-material==8.5.10 pygments==2.19.2
       - name: Deploy
         run: |
           git pull