test: fix Model Validation tests

[kenjis]

Description

There were 6 errors:

1) CodeIgniter\Models\ValidationModelTest::testValidationPlaceholdersSuccess
LogicException: No validation rules for the placeholder: id

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:687
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:138
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:1453
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/ValidationModelTest.php:157
phpvfscomposer:///home/runner/work/CodeIgniter4/CodeIgniter4/vendor/phpunit/phpunit/phpunit:106

2) CodeIgniter\Models\ValidationModelTest::testValidationPlaceholdersFail
LogicException: No validation rules for the placeholder: id

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:687
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:138
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:1453
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/ValidationModelTest.php:168
phpvfscomposer:///home/runner/work/CodeIgniter4/CodeIgniter4/vendor/phpunit/phpunit/phpunit:106

3) CodeIgniter\Models\ValidationModelTest::testValidationWithGroupName
LogicException: No validation rules for the placeholder: id

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:687
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:138
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:1453
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/ValidationModelTest.php:262
phpvfscomposer:///home/runner/work/CodeIgniter4/CodeIgniter4/vendor/phpunit/phpunit/phpunit:106

4) CodeIgniter\Models\ValidationModelTest::testUpdateWithValidation
LogicException: No validation rules for the placeholder: id

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:687
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:138
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:1453
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:745
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Model.php:730
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/ValidationModelTest.php:277
phpvfscomposer:///home/runner/work/CodeIgniter4/CodeIgniter4/vendor/phpunit/phpunit/phpunit:106

5) CodeIgniter\Models\ValidationModelTest::testValidationIncludingErrors
LogicException: No validation rules for the placeholder: id

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:687
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:138
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:1453
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:745
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Model.php:730
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/ValidationModelTest.php:330
phpvfscomposer:///home/runner/work/CodeIgniter4/CodeIgniter4/vendor/phpunit/phpunit/phpunit:106

6) CodeIgniter\Models\ValidationModelTest::testValidationByObject
LogicException: No validation rules for the placeholder: id

/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:687
/home/runner/work/CodeIgniter4/CodeIgniter4/system/Validation/Validation.php:138
/home/runner/work/CodeIgniter4/CodeIgniter4/system/BaseModel.php:1453
/home/runner/work/CodeIgniter4/CodeIgniter4/tests/system/Models/ValidationModelTest.php:343
phpvfscomposer:///home/runner/work/CodeIgniter4/CodeIgniter4/vendor/phpunit/phpunit/phpunit:106

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide