gh-38556: Revert cysignals build constraint
Reverts https://github.com/sagemath/sage/commit/95428a1c31939d8159fbce8f
b0384fa26f0470fe which broke the conda ci.
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URL: https://github.com/sagemath/sage/pull/38556
Reported by: Tobias Diez
Reviewer(s): Dima Pasechnik
