[HttpFoundation] Add peekMultiple method to FlashBag

[alexmerlin]

Q	A
Branch?	6.3
Bug fix?	no
New feature?	no
Deprecations?	no
Tickets	Fix #49659
License	MIT
Doc PR	-

This PR adds the peekMultiple method to FlashBag and AutoExpireFlashBag, as requested in #49659.

[alexmerlin]

Hey @derrabus, thank you for looking into this PR.
Do you have any insight on what should I fix in order to go green with the tests?
From what I see, the tests did not fail, it's just an error that the Process completed with exit code 1.

[andreybolonin]

@alexmerlin As I understand 6.2 is feature freeze stage and no adding new features
You should change 6.3 to 6.4 after 31 may

[derrabus]

Do you have any insight on what should I fix in order to go green with the tests?

I don't think that the failure is related to your changes. You can ignore the red unit tests.