Make "/user/login" page redirect if the current user has signed in (#29583)

Fix #29582 and maybe more.
Maybe fix #29116

services/contexttest/context_tests.go

@@ -7,6 +7,7 @@ package contexttest
 import (
 	gocontext "context"
 	"io"
+	"maps"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
@@ -36,7 +37,7 @@ func mockRequest(t *testing.T, reqPath string) *http.Request {
 	}
 	requestURL, err := url.Parse(path)
 	assert.NoError(t, err)
-	req := &http.Request{Method: method, URL: requestURL, Form: url.Values{}}
+	req := &http.Request{Method: method, URL: requestURL, Form: maps.Clone(requestURL.Query()), Header: http.Header{}}
 	req = req.WithContext(middleware.WithContextData(req.Context()))
 	return req
 }