Update dependency cython to v3.1.6

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
cython (source)	==3.1.5 -> ==3.1.6

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Release Notes

cython/cython (cython)

v3.1.6

Compare Source

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Bugs fixed

• Unicode characters formatted from C integers with f"{value:c}" could result in
  invalid Python string objects since Cython 3.1.0.
  (Github issue :issue:7240)

• cythonize (program and function) now uses concurrent.futures.ProcessPoolExecutor
  instead of multiprocessing.Pool to fix a hang on build failures in parallel builds.
  A possible work-around is to disable parallel builds.
  Patch by Sviatoslav Sydorenko. (Github issue :issue:7183)

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