build dependency: pin @antora/pdf-extension to fixed version 1.0.0-beta.20

Author: hanjianqiao

.github/workflows/merge-build-push.yml

@@ -192,7 +192,7 @@ jobs:
       - name: Install Antora CLI
         run: |
           echo "Installing Antora packages local..."
-          npm install --global antora@3.1.7  @antora/lunr-extension  @antora/pdf-extension  @node-rs/jieba
+          npm install --global antora@3.1.7  @antora/lunr-extension  @antora/pdf-extension@1.0.0-beta.20  @node-rs/jieba
 
       - name: Build English Documentation
         working-directory: ./ivory-doc-builder

.github/workflows/pr-preview.yml

@@ -107,7 +107,7 @@ jobs:
       - name: Install Antora CLI
         run: |
           echo "Installing Antora packages local..."
-          npm install --global antora@3.1.7  @antora/lunr-extension  @antora/pdf-extension  @node-rs/jieba
+          npm install --global antora@3.1.7  @antora/lunr-extension  @antora/pdf-extension@1.0.0-beta.20  @node-rs/jieba
 
       - name: Build English Documentation
         working-directory: ./ivory-doc-builder