Fix GH-16957: Assertion failure in array_shift with self-referencing array

We have an RC1 violation because we're immediately dereferencing and
copying the resulting array in the test ca

Fix GH-16957: Assertion failure in array_shift with self-referencing array

We have an RC1 violation because we're immediately dereferencing and
copying the resulting array in the test case. Instead, transfer the
lifetime using RETVAL_COPY_VALUE and unwrap only after the internal
iterator is reset.

Closes GH-16970.

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