Restore Gleam, Rebar3 and Erlang LS to erlang again

[paulo-ferraz-oliveira]

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... and not specifically bound to a given version (@26). It's possible something changed (for the better) since I started working on the erlang@27 formula, but CI will tell if this change is Ok (locally it seems to be).

Regarding Erlang LS I also contacted one of the maintainers (@plux), and I'm waiting to understand if rebar3 is an actual dependency or just a development one, so I'd maybe hold of on merging until I get an answer, after which I'd add => :build to the formula.

@carlocab, should I up the revision here, since I touched the dependencies again?

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