Refactor tests (#33021)

1. fix incorrect tests, for example: BeanExists doesn't do assert and
shouldn't be used
2. remove unnecessary test functions
3. introduce DumpQueryResult to help to see the database rows during
test (at least I need it)

```
====== DumpQueryResult: SELECT * FROM action_runner_token ======
- # row[0]
  id: 1
  token: xeiWBL5kuTYxGPynHCqQdoeYmJAeG3IzGXCYTrDX
  owner_id: 0
...
```

tests/integration/signin_test.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 	"testing"
 
+	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
@@ -17,6 +18,7 @@ import (
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func testLoginFailed(t *testing.T, username, password, message string) {
@@ -42,7 +44,7 @@ func TestSignin(t *testing.T) {
 	user.Name = "testuser"
 	user.LowerName = strings.ToLower(user.Name)
 	user.ID = 0
-	unittest.AssertSuccessfulInsert(t, user)
+	require.NoError(t, db.Insert(db.DefaultContext, user))
 
 	samples := []struct {
 		username string