docs: Use validateData() to validate POST data only

[obozdag]

Instead of withRequest(), use validateData() to validate POST data only. withRequest() uses $request->getVar() which returns $_GET, $_POST and $_COOKIE data in that order. Newer values override older values. Post values will be overriden by the cookies if they have the same name.

Description
Explain what you have changed, and why.

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

[kenjis]

This warning will be too long.
Why don't you add another warning about this addition, and move it to the top of the section?
Personally $this->validate() is not recommended.

Suggested change

	Instead of withRequest(), use validateData() to validate POST data only. withRequest() uses $request->getVar() which returns $_GET, $_POST and $_COOKIE data in that order. Newer values override older values. Post values will be overriden by the cookies if they have the same name.
	Instead of ``validate()``, use ``validateData()`` to validate POST data only.
	``withRequest()`` uses ``$request->getVar()`` which returns ``$_GET``, ``$_POST``
	or ``$_COOKIE`` data in that order (depending on php.ini
	`request-order <https://www.php.net/manual/en/ini.core.php#ini.request-order>`_).
	Newer values override older values. POST values may be overridden by the
	cookies if they have the same name.

[obozdag]

Thanks for the edit. That is what I was trying to explain. But unfortunately I don't know this markup language used here. I would appreciate if you could do it, please.

[datamweb]

See here it might help you.
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/documentation.rst

[kenjis]

Okay, I sent #8169

[kenjis]

@obozdag I sent another PR to add another warnings in validation and incommingrequest: #8160

[kenjis]

Closed by #8169