Tezt/Tests: add protocol migration test for tolerated_inactivity_period

This MR adds a protocol migration test for tolerated_inactivity_period, as this protocol constant was lowered from 3 to 2 cycles in proto R.

See details in https://docs.google.com/document/d/1CDBhONiUSXchj3etsMImQX1pGGz8lkMCYUnD5XTm1jA/edit?usp=sharing

Manually testing the MR

dune exec tezt/tests/main.exe -- --file protocol_migration.ml -m "tolerated" --info

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