Apply lng2020 to maintainers (#27068)

Hi all,

I've very much enjoyed working on Gitea and was hoping to make it
official by requesting maintainership. 

My [merged PRs
list](https://github.com/go-gitea/gitea/pulls?q=is%3Apr+sort%3Aupdated-desc+author%3Alng2020+is%3Amerged)

Author: lng2020

MAINTAINERS

@@ -56,3 +56,4 @@ Denys Konovalov <kontakt@denyskon.de> (@denyskon)
 Punit Inani <punitinani1@gmail.com> (@puni9869)
 CaiCandong  <1290147055@qq.com> (@caicandong)
 Rui Chen  <rui@chenrui.dev> (@chenrui333)
+Nanguan Lin <nanguanlin6@gmail.com> (@lng2020)