[CI] Update Docker CI · math-comp/odd-order@8468ea5

The following actions uses node12 which is deprecated and will be forced to run on node16: actions/checkout@v2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

Notation natCK is deprecated since mathcomp 2.1.0.

Notation natCK is deprecated since mathcomp 2.1.0.

Notation Cnat is deprecated since mathcomp 2.1.0.

Notation Cnat is deprecated since mathcomp 2.1.0.

Notation conj_Cnat is deprecated since mathcomp 2.1.0.

Notation conj_Cnat is deprecated since mathcomp 2.1.0.

Notation conj_Cnat is deprecated since mathcomp 2.1.0.

Notation truncCK is deprecated since mathcomp 2.1.0.

Notation truncCK is deprecated since mathcomp 2.1.0.

Notation truncCK is deprecated since mathcomp 2.1.0.

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