Array to string warning when spellchecking negated keyword

The MR checks if the array values are an array. If so, it passes the the 0th key to the spellchecker. So the example array in the description is spellchecked as:

$spellcheck_options['keys'][
 0 => 'apple',
 1 => 'banana',
]

Alternatively, it could be removed, but it seems beneficial on balance to spellcheck the negated keyword rather than ignore it.

I don't understand why the MR build pipeline failed. This is a very simple change. I applied the patch locally to 4.3.10 and it applies and resolves the warnings.

Noting that I identified and reported the issue running 4.3.10 but the MR is against 4.x-dev. The code is the same but the line numbers are slightly different.