deploy: Only deploy from pushes to 'master' branch

As we ended up using that and not 'main'

Author: progval

.github/workflows/deploy.yml

@@ -3,7 +3,7 @@ name: Deploy Hugo site to GitHub Pages
 on:
   # Runs on pushes targeting the default branch
   push:
-    branches: ["main", "master"]  # TODO: decide on a final branch name
+    branches: ["master"]
 
   # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch: