Try to fix "View source" and "Edit this page"

These links are still using `master` instead of `main`.

The redirecto works for "View source" but does not work for "Edit this page".

_output.yml

@@ -1,7 +1,9 @@
 bookdown::bs4_book:
   theme:
     primary: "#4D6F8D"
-  repo: https://github.com/jennybc/happy-git-with-r
+  repo:
+      base: https://github.com/jennybc/happy-git-with-r
+      branch: main
   includes:
     in_header: [ga_script.html]
 bookdown::gitbook: