maint(ci): avoid cython 0.29.31 under PyPy

[oscarbenjamin]

References to other Issues or PRs

#23061 (comment)

Brief description of what is fixed or changed

The PyPy optional dependency job avoids Cython 0.29.31 which fails to build SciPy 1.8.1. This is probably an upstream bug in either Cython or SciPy.

Other comments

For a brief moment the CPython 3.11.0b5 release hit CI and we actually had everything pass on master (25cbe76). Within hours though two different problems emerged and the next merge to master (dc86589) has two jobs failing both in the build of SciPy.

It's not clear yet what the problems are that cause this or if they are related. They seem to be because they both show the same error pointing at

      FAILED: scipy/stats/_stats.cpython-311-x86_64-linux-gnu.so.p/_stats.c
      /opt/hostedtoolcache/Python/3.11.0-beta.5/x64/bin/python /tmp/pip-req-build-ftutz8xt/scipy/_build_utils/cythoner.py ../../scipy/stats/_stats.pyx scipy/stats/_stats.cpython-311-x86_64-linux-gnu.so.p/_stats.c
      
      Error compiling Cython file:
      ------------------------------------------------------------
      ...
          return np.array(result, dtype=np.int64)
      
      
      @cython.wraparound(False)
      @cython.boundscheck(False)
      def _weightedrankedtau(ordered[:] x, ordered[:] y, intp_t[:] rank, weigher, bool additive):
      ^

However the two jobs use different versions of everything. The PyPy job installs cython, numpy and scipy all from pip to retrieve the latest versions. The only thing that seems to have changed there is the release of Cython 0.29.31.

The 3.11 job now uses CPython 3.11.0b5 and installs cython, numpy and scipy from git master/main. The Cython master branch currently reports as Cython-3.0.0a10. It's not clear if there has been a change in Cython master or a change in SciPy main that has caused this to fail but since the error message is similar to the one seen with Cython 0.29.31 maybe they are releated.

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#### References to other Issues or PRs
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https://github.com/sympy/sympy/issues/23061#issuecomment-1197517304

#### Brief description of what is fixed or changed

The PyPy optional dependency job avoids Cython 0.29.31 which fails to build SciPy 1.8.1. This is probably an upstream bug in either Cython or SciPy.

#### Other comments

For a brief moment the CPython 3.11.0b5 release hit CI and we actually had everything pass on master (25cbe76557c2685afc209dcca13c9e0ec3f9a68e). Within hours though two different problems emerged and the next merge to master (dc86589ada8739dfdbf3bf014e6361bc4a42ff70) has two jobs failing both in the build of SciPy.

It's not clear yet what the problems are that cause this or if they are related. They seem to be because they both show the same error pointing at
```
      FAILED: scipy/stats/_stats.cpython-311-x86_64-linux-gnu.so.p/_stats.c
      /opt/hostedtoolcache/Python/3.11.0-beta.5/x64/bin/python /tmp/pip-req-build-ftutz8xt/scipy/_build_utils/cythoner.py ../../scipy/stats/_stats.pyx scipy/stats/_stats.cpython-311-x86_64-linux-gnu.so.p/_stats.c
  
      Error compiling Cython file:
      ------------------------------------------------------------
      ...
          return np.array(result, dtype=np.int64)
  
  
      @cython.wraparound(False)
      @cython.boundscheck(False)
      def _weightedrankedtau(ordered[:] x, ordered[:] y, intp_t[:] rank, weigher, bool additive):
      ^
```
However the two jobs use different versions of everything. The PyPy job installs cython, numpy and scipy all from pip to retrieve the latest versions. The only thing that seems to have changed there is the release of Cython 0.29.31.

The 3.11 job now uses CPython 3.11.0b5 and installs cython, numpy and scipy from git master/main. The Cython master branch currently reports as Cython-3.0.0a10. It's not clear if there has been a change in Cython master or a change in SciPy main that has caused this to fail but since the error message is similar to the one seen with Cython 0.29.31 maybe they are releated.


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[oscarbenjamin]

This doesn't work because I think when SciPy builds it installs its own version of Cython and so still picks up 0.29.31 even if we don't install that version.

[oscarbenjamin]

I've opened a SciPy issue: scipy/scipy#16723

For now I'll make the PyPy job an allowed failure in CI (the 3.11 job already is).

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