Upgrade ubuntu from 20.04 to 24.04

As 20.04 is deprecated will be removed on 2025-04-15:
actions/runner-images#11101

Author: ramsayleung

.github/workflows/gh-pages.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   deploy:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v2
         with: