Fix: ignore 429 htmlproofer (too many requests normally github related)

Author: lwasser

.github/workflows/build-book.yml

@@ -56,7 +56,7 @@ jobs:
           directory: ./_build/html
           arguments: |
             --ignore-files "/.+\/_static\/.+/"
-            --ignore-status-codes "0, 200, 301, 401, 403, 503"
+            --ignore-status-codes "0, 200, 301, 401, 403, 429, 503"
             --ignore-urls "https://github.com/pyOpenSci/software-review/issues/18#issuecomment-581752433"
 
       # Save html as artifact