Fix unit tests assertion parameters for expected and actual values

## Expected behavior
In unit tests, `Assert` methods such as `Assert.AreEqual(value, otherValue)` should have the first parameter be the expected value, second parameter the actual value.

## Current behavior
Some correct usage, mostly backwards. [Example](https://github.com/CommunityToolkit/dotnet/blob/main/tests/CommunityToolkit.Mvvm.UnitTests/Test_ICommandAttribute.cs#L20)