package/python-multidict: bump to version 4.7.5

Bugfix release, fixing a number of issues. From the CHANGES file:

- Fixed creating and updating of MultiDict from a sequence of pairs and
  keyword arguments.  Previously passing a list argument modified it
  inplace, and other sequences caused an error.
  https://github.com/aio-libs/multidict/issues/457

- Fixed comparing with mapping: an exception raised in the __len__ method caused raising a SyntaxError.
  https://github.com/aio-libs/multidict/issues/459

- Fixed comparing with mapping: all exceptions raised in the __getitem__
  method were silenced.
  https://github.com/aio-libs/multidict/issues/460

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Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
[Peter: extend commit message]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>