Enable PR-triggered workflow runs on master

Author: nevalsar

.github/workflows/jekyll-github-pages-deploy.yml

@@ -10,6 +10,8 @@ on:
   # Runs on pushes targeting the default branch
   push:
     branches: ["master", "deployment-test"]
+  pull_request:
+    branches: ["master"]
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch: