.github(workflows), Dockerfile: bump Nim from 1.6.4 to 1.6.10

[ee7]

See the release blog posts:

• https://nim-lang.org/blog/2022/05/05/version-166-released.html
• https://nim-lang.org/blog/2022/09/27/version-168-released.html
• https://nim-lang.org/blog/2022/11/23/version-1610-released.html

and changes since 1.6.4:

• https://github.com/nim-lang/Nim/compare/v1.6.4...v1.6.6
• https://github.com/nim-lang/Nim/compare/v1.6.6...v1.6.8
• https://github.com/nim-lang/Nim/compare/v1.6.8...v1.6.10

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Upstream: https://github.com/exercism/nim-docker-base/actions/runs/3532170682/jobs/5926197352#step:8:187