Assigning command call is allowed where rejected in parse.y

[tompng]

These command calls are rejected in parse.y but accepted in prism

1 if a = b c
1 and a = b c
a = b c and 1

[Earlopain]

I fixed the first two cases in https://github.com/ruby/prism/pull/3654 but the last one is still up for grabs