test: make REPL test pass in coverage mode

Make a REPL tab completion test pass in coverage mode by using
`Uin` as the common prefix of all `Uint*Array` globals instead
of `co` which could be a prefix for `console` and `coverage`,
so it doesn't expand the way it's expected to in coverage mode.

PR-URL: https://github.com/nodejs/node/pull/17082


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>