inline gitpod image (go-gitea#21494)

fix go-gitea#21492

Co-authored-by: 6543 <[email protected]>

Author: techknowlogick

docs/content/doc/developers/hacking-on-gitea.en-us.md

@@ -23,7 +23,7 @@ menu:
 
 To get a quick working development environment you could use Gitpod.
 
-[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/go-gitea/gitea)
+[![Open in Gitpod](/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/go-gitea/gitea)
 
 ## Installing go