fix(SymfonyConstraintAnnotationReader): disallow null if NotNull attribute is present

[jeremyVignelles]

Q	A
Bug fix?	yes
New feature?	no
Deprecations?	no
Issues	Fix #2309

if a property is set as something like this:

#[OA\Property()]
#[Assert\NotNull(groups: ['validation'])]
private ?string $prop = null;

that property will be marked as nullable AND required.
This PR ensures that the nullable property is also set appropriately when a NotNull is set

NOTE: PHPUnit already fails on master

[DjordyKoert]

Could you update with master? :)

[jeremyVignelles]

Done, unit tests and code style fixed, commits squashed into one :)
You're good to go :)

[DjordyKoert]

Thank you :)