update ci for test of PRs

Author: herbetom

.github/workflows/test-pull_requests.yml

@@ -10,7 +10,7 @@ on:
 # A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
@@ -22,7 +22,7 @@ jobs:
       - name: Setup Hugo
         uses: peaceiris/actions-hugo@v2
         with:
-          hugo-version: '0.75.1'
+          hugo-version: '0.91.2'
           extended: true
 
       - name: Hugo Version