Remove if/else from modbus test cases

[janiversen]

Breaking change

Proposed change

We should avoid if/else in the test cases when combined with parametrisation. This PR updates all modbus test cases.

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[probot-home-assistant]

Hey there @adamchengtkc, @vzahradnik, mind taking a look at this pull request as its been labeled with an integration (modbus) you are listed as a codeowner for? Thanks!
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[janiversen]

@MartinHjelmare you asked me to avoid if/else in the test cases (my latest modbus PR, with the new configuration), so I went ahead and updated all test cases to this new style. I hope you like it.

[MartinHjelmare]

Great!

[MartinHjelmare]

Nice!