Fix AA iteration order dependency in testaa2.d

[n8sh]

Blocking dlang/druntime#3148 (comment)

A DMD test is failing because it depends on a specific AA traversal order. I am inclined to consider that erroneous based on https://dlang.org/spec/hash-map.html: "The built-in associative arrays do not preserve the order of the keys inserted into the array. In particular, in a foreach loop the order in which the elements are iterated is typically unspecified."

Test runnable/testaa2.d failed: 
expected:
----
foo()
foo() 2
foo() 3
foo() 4
c["foo"] = 3
c["bar"] = 4
Success
----
actual:
----
foo()
foo() 2
foo() 3
foo() 4
c["bar"] = 4
c["foo"] = 3
Success

[dlang-bot]

Thanks for your pull request, @n8sh!

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[MoonlightSentinel]

Please remove this output and add appropriate asserts (the test is compiled with enabled assertions).

[n8sh]

Done

[MoonlightSentinel]

Thanks