Update gh-pages.yml

Author: vivian1912

.github/workflows/gh-pages.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Prepare build environment
       run: |
         sudo apt install python3-pip python3-dev python3-setuptools
-        sudo pip3 install -U mkdocs==1.3.0 pygments pymdown-extensions
+        sudo pip3 install -U mkdocs==1.3.0 pygments==2.17.2 pymdown-extensions --break-system-packages
 
     - name: Build the document
       run: mkdocs build