smart rollup: add inbox migration test

Context

Adds a test to make sure that a l1 migration does not break the smart rolllup inbox.

The first test checks that the inbox can still receive internal and external message, while the second test to send tickets by internal message.

issue #3703

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR