import errors with ops-scenario 7.x

Event class is not there in ops-scenario in 7.x and so can see the below error whenever pytest-interface-tester is used.
`ImportError: cannot import name 'Event' from 'scenario'`

https://github.com/canonical/pytest-interface-tester/blob/main/pyproject.toml#L25 should add `<7` as well.

Start at pyproject.toml line 25 and inspect the ops-scenario dependency constraint. Run the reported pytest-interface-tester import path with ops-scenario 7.x to confirm the Event ImportError. Done means the dependency specification excludes the incompatible 7.x versions and the relevant test or installation check passes.

Written by the indexing model from the issue text.