fix(ci): use Docker network hostname for docs runner checkout

The act_runner and gitea containers share the git_default Docker
network. Use http://gitea:3000 (container DNS name) instead of
localhost, which resolves to the runner container itself.

docs/book.toml

@@ -2,6 +2,7 @@
 title = "Kindred Create Documentation"
 authors = ["Kindred Systems LLC"]
 language = "en"
+multilingual = false
 src = "src"
 
 [build]