chore: Only include Credo in dev and test environments

mix.exs

@@ -52,7 +52,7 @@ defmodule MedicalTranscription.MixProject do
       {:jason, "~> 1.2"},
       {:dns_cluster, "~> 0.1.1"},
       {:plug_cowboy, "~> 2.5"},
-      {:credo, "~> 1.7.3"},
+      {:credo, "~> 1.7.3", only: [:dev, :test]},
       {:audio_tagger, git: "https://github.com/headwayio/audio_tagger.git"},
       {:progress_bar, "~> 3.0"},
       {:membrane_core, "~> 1.0"},