update peaceiris ghpages to v4

Author: trevorcampbell

.github/workflows/deploy_main_preview.yml

@@ -38,7 +38,7 @@ jobs:
 
        # Push the book's HTML to github-pages
       - name: GitHub Pages action
-        uses: peaceiris/actions-gh-pages@v3.8.0
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: source/_build/html

.github/workflows/deploy_pr_preview.yml

@@ -48,7 +48,7 @@ jobs:
 
        # Push the book's HTML to github-pages
       - name: GitHub Pages action
-        uses: peaceiris/actions-gh-pages@v3.8.0
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: source/_build/html
@@ -71,7 +71,7 @@ jobs:
           website_diff --old dev --new pull${{ github.event.number }} --diff diff${{ github.event.number }}
 
       - name: GitHub Pages action to push diff
-        uses: peaceiris/actions-gh-pages@v3.8.0
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: diff${{ github.event.number }}

.github/workflows/update_book.yml

@@ -29,7 +29,7 @@ jobs:
           
       # Push updated website, clean out old commits
       - name: Update website
-        uses: peaceiris/actions-gh-pages@v3.8.0
+        uses: peaceiris/actions-gh-pages@v4
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./