Fix language switch for install page (#16043)

Signed-off-by: a1012112796 <1012112796@qq.com>

routers/routes/install.go

@@ -103,7 +103,7 @@ func InstallRoutes() *web.Route {
 	r.Get("/", routers.Install)
 	r.Post("/", web.Bind(forms.InstallForm{}), routers.InstallPost)
 	r.NotFound(func(w http.ResponseWriter, req *http.Request) {
-		http.Redirect(w, req, setting.AppURL, 302)
+		http.Redirect(w, req, setting.AppURL, http.StatusFound)
 	})
 	return r
 }