Fix CI (run gitea without root previleges) (#569)

CI is broken due to gitea upstream changes in deployment; may not run as root.
I have not tested if this actually fixes things, for upstream reference see f0bd1e9896 (diff-b54b39f1afced2465e1f3641db9d5bbf4f3a7fcf890996dfedd3c197bcb7f8c7)

I also switched from `:latest` to `:dev`, see https://github.com/go-gitea/gitea/pull/16421

edit: sorry for the messy commit list below, it's actually just a single commit.
Co-authored-by: Norwin <git@nroo.de>
Reviewed-on: https://gitea.com/gitea/go-sdk/pulls/569
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>

.drone.yml

@@ -12,8 +12,9 @@ workspace:
 
 steps:
 - name: gitea
-  image: gitea/gitea:latest
+  image: gitea/gitea:dev
   detach: true
+  user: gitea
   commands:
   - mkdir -p /tmp/conf/
   - mkdir -p /tmp/data/