Update CI and README · math-comp/real-closed@0629f87

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Notation nosimpl is deprecated since mathcomp 2.4.

Notation nosimpl is deprecated since mathcomp 2.4.

Notation ler_paddl is deprecated since mathcomp 1.17.0.

Notation ler_paddl is deprecated since mathcomp 1.17.0.

Notation ler_paddl is deprecated since mathcomp 1.17.0.

Notation ler_pmulr is deprecated since mathcomp 1.17.0.

Notation ler_addl is deprecated since mathcomp 1.17.0.

Notation ler_pmulr is deprecated since mathcomp 1.17.0.

Notation ler_pmulr is deprecated since mathcomp 1.17.0.

Notation ler_norm_add is deprecated since mathcomp 1.17.0.

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