Add failing test case for issue #1

[voltrevo]

#1 demonstrates a program which behaves incorrectly.

Solving this wouldn't be a good first issue, but adding a failing test case for it is.

All you have to do is add a file like this: https://github.com/voltrevo/ValueScript/blob/main/inputs/failing/assignmentEvalOrder.ts. (To be clear, test_output! is the incorrect version that is currently produced, not what the output should be. Instead, just comment below about what it should be instead.)

There's a github action to run the tests, so you don't even need to run this locally to validate it :).

@mlajtos (others welcome too)