docker: chown only for the frist time (#5422)

docker/s6/gogs/setup

@@ -19,5 +19,8 @@ ln -sfn /data/gogs/data ./data
 # Backward Compatibility with Gogs Container v0.6.15
 ln -sfn /data/git /home/git
 
-chown -R git:git /data /app/gogs ~git/
+# Only chown for the first time, '/data/gogs/conf/app.ini' must exist inside Docker after installation
+if ! test -d /data/gogs/conf/app.ini; then
+	chown -R git:git /data /app/gogs ~git/
+fi
 chmod 0755 /data /data/gogs ~git/