Add test coverage for modbus switch (coil part) (#40696)

* Prepare test code for complex devices.

push entity_id to conftest, to make it common for all devices.

Add device to base_setup.

* Add test coverage for modbus switch (coil part).

* Update .coveragerc

* Update .coveragerc

Co-authored-by: Chris Talkington <chris@talkingtontech.com>