maint: make python-flint work with Cython 3.2

[oscarbenjamin]

Followup and proper fix after

#337

[oscarbenjamin]

There was a test failure in the pyodide build:

../.venv-pyodide/lib/python3.13/site-packages/flint/test/test_docstrings.py::test_docstrings[flint.types._gr.gr_real_qqbar_ctx.new] PASSED
Pyodide has suffered a fatal error. Please report this to the Pyodide maintainers.
The cause of the fatal error was:
RuntimeError: memory access out of bounds
    at wasm://wasm/020eeec2:wasm-function[9770]:0x4886b7
    at wasm://wasm/02dcec9e:wasm-function[15603]:0x927527
    at wasm://wasm/02dcec9e:wasm-function[15587]:0x926fb4
    at wasm://wasm/02dcec9e:wasm-function[15191]:0x8ff44a
    at wasm://wasm/02f907de:wasm-function[424]:0xc06aa
    at wasm://wasm/02f907de:wasm-function[680]:0xee5bb
    at wasm://wasm/020eeec2:wasm-function[2306]:0x1b8b1d
    at wasm://wasm/02f907de:wasm-function[687]:0xef141
    at wasm://wasm/020eeec2:wasm-function[2306]:0x1b8b1d
    at wasm://wasm/020eeec2:wasm-function[1962]:0x1a0d0a {
  pyodide_fatal_error: true
}

I don't think that is caused by the changes here. Will rerun to see if this is an intermittent failure.

[oscarbenjamin]

https://github.com/flintlib/python-flint/actions/runs/19296682119/job/55180319869

[oscarbenjamin]

The same test has failed again in the same way.