no longer compatible:
```
File "/build/boto-2.49.0/tests/unit/utils/test_utils.py", line 88, in hmac_hashfunc
return hmac.new(b'mysecretkey', msg)
File "/nix/store/x3655l9x6b5khxzzl0s2zg1kn0qr3zfs-python3-3.9.0/lib/python3.9/hmac.py", line 170, in new
return HMAC(key, msg, digestmod)
File "/nix/store/x3655l9x6b5khxzzl0s2zg1kn0qr3zfs-python3-3.9.0/lib/python3.9/hmac.py", line 56, in __init__
raise TypeError("Missing required parameter 'digestmod'.")
TypeError: Missing required parameter 'digestmod'.
```
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