Update cython requirement from <4,>=3.1 to >=3.1.8,<4

[dependabot]

Updates the requirements on cython to permit the latest version.

Changelog

Sourced from cython's changelog.

3.1.8 (2026-01-03)

Bugs fixed

• Assignment expressions used in comprehensions could look at the wrong scope, thus using different variables and different data. (Github issue :issue:6547)

• Some internal C symbols were not declared as static, preventing static linking of multiple modules. Patch by Yury Popov. (Github issue :issue:7310)

• Accidentally using except + in C mode did not raise a compile error but generated invalid C code leading to obscure error messages. Patch by user202729. (Github issue :issue:6560)

3.1.7 (2025-11-12)

Bugs fixed

• Unicode characters formatted from C integers with padding, as in f"{value:XXc}", could result in invalid Python string objects since Cython 3.1.0. Also, lone surrogates failed to format in this way. (Github issue :issue:7298)

• Assigning nested structs from a list of structs (item by item) could crash Cython. (Github issue :issue:7308)

• Cython incorrectly called PyList_GetItemRef() in PyPy and GraalPython before Py3.13. (Github issue :issue:7269)

• Trying to instantiate internal types used by Cython is now prohibited. (Github issue :issue:7263)

3.1.6 (2025-10-23)

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)

... (truncated)

Commits

• 94ea88b Update changelog.
• b975bf2 Prepare release of 3.1.8.
• b14bbad Update changelog.
• a950bdf Fix some assignment expression scoping (#6553)
• 6860abd Update changelog.
• 7d41252 Add a missing check for C++ mode when including the C++ headers (GH-7329)
• 3de0b32 Update changelog.
• 80df88a Fix static-const in builtins protos (GH-7331)
• 9be46dc Update changelog.
• 44e0951 Prepare release of Cython 3.1.7.
• Additional commits viewable in compare view

Most Recent Ignore Conditions Applied to This Pull Request

Dependency Name	Ignore Conditions
cython	[>= 3.2.dev0, < 3.3]

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[Kijewski]

@dependabot ignore this minor version

[dependabot]

OK, I won't notify you about version 3.1.x again, unless you re-open this PR.

[Kijewski]

@dependabot ignore this major version

[dependabot]

OK, I won't notify you about version 3.x.x again, unless you re-open this PR.