dev-cmd/update-maintainers: fix undefined method

[ZhongRuoyu]

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This should fix Error: undefined method `slice!' for #<Hash:0x0000000003c557a8> from https://github.com/Homebrew/brew/actions/runs/4659983623/jobs/8247503227#step:6:74.

[apainintheneck]

Out of curiosity, do we know why this broke in the first place? The update-maintainers.rb file hasn't been touched in a while.

Edit: Maybe it was a transitive require somewhere else before?

[ZhongRuoyu]

Edit: Maybe it was a transitive require somewhere else before?

I think so too. This run from 3e2c713 was the last good run, and this from e5c0fb4 was the first bad run. That should narrow down the search range to b180133 (#14917) and e5c0fb4 (#14892) but I didn't see any suspicious requires getting removed. 🤔

[MikeMcQuaid]

Thanks @ZhongRuoyu!