Gleam compile error if dependency has dev dependencies that are not fetched by mix

[spicychickensauce]

While I could resolve #46 via workarounds, this one is actually holding me back from moving forward.

I get this error when trying to compile a project with a (git) gleam dependency:

3> error: Unknown module
3>     ┌─ ./test/my_app_test.gleam:128:5
3>     │
3> 128 │     envoy.get("MAX_NODES") |> result.try(int.parse) |> result.unwrap(30_000)
3>     │     ^^^^^
3>
3> No module has been found with the name `envoy`.
3> could not compile dependency :my_app, "mix compile" failed.

my_app has a dev dependency on envoy:

[dev-dependencies]
envoy = ">= 1.1.0 and < 2.0.0"

It is translated into this mix.exs:

{:envoy, ">= 1.1.0 and < 2.0.0",
   [only: [:dev, :test], runtime: false]},

But I think mix doesn't fetch test / dev dependencies of dependencies, so then gleam fails to compile.
But why does it even try to compile the test/ folder? shouldn't it only compile the src/ folder?

(I hope elixir-lang/elixir#14262 will solve that too, but until that one is merged, I'll try my luck here)