Add workaround for GitHub doc url's returning 403

Author: detrumi

book/book.toml

@@ -16,3 +16,7 @@ additional-js = ["mermaid.min.js", "mermaid-init.js"]
 follow-web-links = true
 warning-policy = "error"
 optional = true
+
+# Workaround for GitHub docs returning 403 response: https://github.com/github/docs/issues/17358
+[output.linkcheck.http-headers]
+"https://help.github.com" = ["accept-encoding: deflate, gzip, br"]