Complete rustpython-unicode isolation: case mapping, casing predicates, sre parity - #8237

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: wasmerio/setup-wasmer@24b15c95293d23f89c68bd40dac76338f773e924. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/