[Hackday][2.7] Added deprecated notes to '_method' and '_scheme' route requirements

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | no
| Fixed tickets | [#12641, #12640]
| License       | MIT
| Doc PR        |
please format it this way: https://github.com/symfony/symfony/blob/c6cc3ebfbe9e93210632115f7cd8f5eb8ede8a74/src/Symfony/Component/HttpKernel/Debug/ErrorHandler.php#L14