sh -> plain because comamnd output is not shell command

Author: aster-void

docs/3-web-servers/10-git-github-init/index.mdx

@@ -197,7 +197,7 @@ Are you sure you want to continue connecting (yes/no/[fingerprint])?
 
 :::
 
-```sh
+```plain
 Hi (ユーザー名)! You've successfully authenticated, but GitHub does not provide shell access.
 ```