refactor: fix Security test fail by itself

[paulbalandan]

Description
Running SecurityTest by itself leads to failures, which means it is not isolated enough and dependent on other tests.

❯ vendor/bin/phpunit --filter SecurityTestPHPUnit 11.5.55 by Sebastian Bergmann and contributors.Runtime: PHP 8.5.3 with Xdebug 3.5.1Configuration: /Users/paul/Workspace/CodeIgniter4/phpunit.xml.dist........E.E.E......FFF....... 29 / 29 (100%)Time: 00:02.360, Memory: 82.00 MBThere were 3 errors:1) CodeIgniter\Security\SecurityTest::testCSRFVerifyHeaderReturnsSelfOnMatchCodeIgniter\Security\Exceptions\SecurityException: The action you requested is not allowed./Users/paul/Workspace/CodeIgniter4/system/Security/Security.php:263/Users/paul/Workspace/CodeIgniter4/tests/system/Security/SecurityTest.php:1702) CodeIgniter\Security\SecurityTest::testCSRFVerifyJsonReturnsSelfOnMatchCodeIgniter\Security\Exceptions\SecurityException: The action you requested is not allowed./Users/paul/Workspace/CodeIgniter4/system/Security/Security.php:263/Users/paul/Workspace/CodeIgniter4/tests/system/Security/SecurityTest.php:2063) CodeIgniter\Security\SecurityTest::testCSRFVerifyPutBodyReturnsSelfOnMatchCodeIgniter\Security\Exceptions\SecurityException: The action you requested is not allowed./Users/paul/Workspace/CodeIgniter4/system/Security/Security.php:263/Users/paul/Workspace/CodeIgniter4/tests/system/Security/SecurityTest.php:242--There were 3 failures:1) CodeIgniter\Security\SecurityTest::testGetPostedTokenReturnsTokenFromHeaderFailed asserting that null is identical to '8b9218a55906f9dcc1dc263dce7f005a'./Users/paul/Workspace/CodeIgniter4/tests/system/Security/SecurityTest.php:3462) CodeIgniter\Security\SecurityTest::testGetPostedTokenReturnsTokenFromJsonBodyFailed asserting that null is identical to '8b9218a55906f9dcc1dc263dce7f005a'./Users/paul/Workspace/CodeIgniter4/tests/system/Security/SecurityTest.php:3553) CodeIgniter\Security\SecurityTest::testGetPostedTokenReturnsTokenFromFormBodyFailed asserting that null is identical to '8b9218a55906f9dcc1dc263dce7f005a'./Users/paul/Workspace/CodeIgniter4/tests/system/Security/SecurityTest.php:364ERRORS!Tests: 29, Assertions: 34, Errors: 3, Failures: 3.Generating code coverage report in Clover XML format ... done [00:00.463]Generating code coverage report in HTML format ... done [00:03.204]

Ref: #9968

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide