cython master branch cannot build HEAD of symengine.py

[bjodah]

Cythonization error:

      [ 50%] Cythonizing /tmp/pip-install-qgianthy/symengine_7919c2d002ce4afe9fea82e7bdc6d9ec/build/lib.linux-x86_64-cpython-311/symengine/lib/symengine_wrapper.pyx
      performance hint: symengine_wrapper.pyx:5072:5: Exception check on '_ctypes_callback_lambda_real' will always require the GIL to be acquired.
      Possible solutions:
          1. Declare '_ctypes_callback_lambda_real' as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
          2. Use an 'int' return type on '_ctypes_callback_lambda_real' to allow an error code to be returned.
      performance hint: symengine_wrapper.pyx:5082:5: Exception check on '_ctypes_callback_llvm_real' will always require the GIL to be acquired.
      Possible solutions:
          1. Declare '_ctypes_callback_llvm_real' as 'noexcept' if you control the definition and you're sure you don't want the function to raise exceptions.
          2. Use an 'int' return type on '_ctypes_callback_llvm_real' to allow an error code to be returned.
      
      Error compiling Cython file:
      ------------------------------------------------------------
      ...
      
          @property
          def is_Equality(self):
              return True
      
          func = __class__
                 ^
      ------------------------------------------------------------
      
      symengine_wrapper.pyx:1627:11: undeclared name not builtin: __class__
      gmake[2]: *** [symengine/lib/CMakeFiles/symengine_wrapper.dir/build.make:76: symengine/lib/symengine_wrapper.cpp] Error 1
      gmake[1]: *** [CMakeFiles/Makefile2:112: symengine/lib/CMakeFiles/symengine_wrapper.dir/all] Error 2
      gmake: *** [Makefile:136: all] Error 2
      error: error building project
      [end of output]

I haven't yet checked to see if it's something we are doing wrong, or if this is a regression in Cython.