PR #2062 fixes copy for unicode keys. However, the change breaks keys
with question marks. Here is an alternative fix that works for both
emojis and question marks.
I notice this when running the test suite of aiobotocore. One of the
tests [1] is broken with moto >= 1.3.8.
[1] https://github.com/aio-libs/aiobotocore/blob/0.10.3/tests/test_basic_s3.py#L314-L329