Fix session key conflict with database keyword (#28613)

This is a regression from #28220 .
`builder.Cond` will not add `` ` `` automatically but xorm method
`Get/Find` adds `` ` ``.

This PR also adds tests to prevent the method from being implemented
incorrectly. The tests are added in `integrations` to test every
database.

tests/integration/session_test.go

@@ -0,0 +1,37 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/auth"
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/tests"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_RegenerateSession(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	key := "new_key890123456"  // it must be 16 characters long
+	key2 := "new_key890123457" // it must be 16 characters
+	exist, err := auth.ExistSession(db.DefaultContext, key)
+	assert.NoError(t, err)
+	assert.False(t, exist)
+
+	sess, err := auth.RegenerateSession(db.DefaultContext, "", key)
+	assert.NoError(t, err)
+	assert.EqualValues(t, key, sess.Key)
+	assert.Len(t, sess.Data, 0)
+
+	sess, err = auth.ReadSession(db.DefaultContext, key2)
+	assert.NoError(t, err)
+	assert.EqualValues(t, key2, sess.Key)
+	assert.Len(t, sess.Data, 0)
+}