Fixes hub github actions to run on PRs

We want to build the site for any contrib changes. But we
only want to deploy once merged to main. This adds
that conditional logic.

.github/workflows/docusaurus-gh-pages.yml

@@ -4,7 +4,6 @@ name: Deploy Docusaurus with GitHub Pages dependencies preinstalled
 on:
   # Runs on pushes targeting the default branch & contrib subdirectory
   push:
-    branches: ["user_contrib", "main"]
     paths:
       - 'contrib/**'
 
@@ -25,7 +24,7 @@ concurrency:
 
 jobs:
   branch-build:
-    if: GITHUB_REF_NAME != 'main'
+    if: ${{ github.ref != 'refs/heads/main' }}
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
@@ -64,7 +63,7 @@ jobs:
         run: yarn build
       # 👆 Build steps
   deploy:
-    if: GITHUB_REF_NAME == 'main'
+    if: ${{ github.ref == 'refs/heads/main' }}
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}