CSRF warning docs on Request::enableHttpMethodParameterOverride()

[HttpFoundation] fixed the docs so that it gives some explanation about how you are vulnerable to CSRF when you enable the httpMethodeParameterOverride
minor #12168 [HttpFoundation] CSRF warning docs on Request::enableHttpMethodParameterOverride() (Kristof Van Cauwenbergh)

This PR was merged into the 2.3 branch.

Discussion
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[HttpFoundation] CSRF warning docs on Request::enableHttpMethodParameterOverride()

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12043
| License       | MIT
| Doc PR        | /

Since I wanted to understand this issue I did some research and altered the comment block. Is this a clear enough explanation or does it need more?

Commits
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deb70ab CSRF warning docs on Request::enableHttpMethodParameterOverride()