chore(docker): append cspell ignore line to ignore spell check of `libcu` and `libnv`

[youtalk]

Description

This PR has appended cspell ignore line to ignore spell check of libcu and libnv. After this PR merged, I expect all CI checks to work properly.

Tests performed

Not applicable.

Effects on system behavior

Not applicable.

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[mitsudome-r]

Thanks for the PR! LGTM