Add specs for evaluation order during assignment

[dushyantss]

This PR adds specs for Bug #4443

From:

• Write specs for new Ruby 3.1 features and changes #923

Multiple assignment evaluation order has been made consistent with
single assignment evaluation order. With single assignment, Ruby
uses a left-to-right evaluation order. With this code:

foo[0] = bar
The following evaluation order is used:

foo
bar
[]= called on the result of foo
In Ruby before 3.1.0, multiple assignment did not follow this
evaluation order. With this code:

foo[0], bar.baz = a, b
Versions of Ruby before 3.1.0 would evaluate in the following
order

a
b
foo
[]= called on the result of foo
bar
baz= called on the result of bar
Starting in Ruby 3.1.0, the evaluation order is now consistent with
single assignment, with the left-hand side being evaluated before
the right-hand side:

foo
bar
a
b
[]= called on the result of foo
baz= called on the result of bar
[Bug #4443]

[eregon]

Looks great, thank you!