Update path to docs theme file (go-gitea#23502) (go-gitea#23505)

Backport go-gitea#23502 by @techknowlogick

The branch name for the theme was updated to main

Co-authored-by: techknowlogick <[email protected]>

Author: GiteaBot

docs/Makefile

@@ -1,6 +1,6 @@
 THEME := themes/gitea
 PUBLIC := public
-ARCHIVE := https://dl.gitea.io/theme/master.tar.gz
+ARCHIVE := https://dl.gitea.com/theme/main.tar.gz
 
 HUGO_PACKAGE := github.com/gohugoio/[email protected]