Update CI config for main

Author: alexcrichton

.github/workflows/main.yml

@@ -144,4 +144,4 @@ jobs:
           git add .
           git -c user.name='ci' -c user.email='ci' commit -m init
           git push -f -q https://git:${{ secrets.github_token }}@github.com/${{ github.repository }} HEAD:gh-pages
-        if: github.event_name == 'push' && github.event.ref == 'refs/heads/master'
+        if: github.event_name == 'push' && github.event.ref == 'refs/heads/main'