Get pandoc release manually from GitHub

.github/workflows/docs.yml

@@ -36,7 +36,9 @@ jobs:
     - name: Install apt-get dependencies
       run: |
         sudo apt-get update
-        sudo apt-get -qq install pandoc
+        curl --silent --location --remote-name https://github.com/jgm/pandoc/releases/download/3.1.6.2/pandoc-3.1.6.2-1-amd64.deb
+        # sudo apt-get -qq install pandoc  # Ubuntu 22.04's pandoc is too old: 2.9.2.x
+        sudo apt-get install ./pandoc-*amd64.deb
 
     - name: Check docstrings
       run: |