Proto/Adaptive inflation: EMA integration test

Context

Fix #5658 (closed)

Adds a test for the code of MR !9002 (merged) on which this MR is stacked.

This MR only tests that voting On has an effect on the EMA. For more complete integration testing of the adaptive inflation activation code, see !9068 (merged) (which is stacked on top of this MR).

Manually testing the MR

dune exec src/proto_alpha/lib_protocol/test/integration/main.exe -- --file test_adaptive_inflation_launch.ml

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