CI: Specify Erlang vsn for macOS

Author: jessestimpson

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
       - name: Install
         run: |
           brew update
-          brew install erlang elixir
+          brew install erlang@27 elixir
       - name: Install dependencies
         run: mix deps.get
       - name: Compile and check warnings