CI: Specify Erlang vsn for macOS

Author: jessestimpson

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
 jobs:
   linux:
     runs-on: ubuntu-latest
-    name: Linux ${{ matrix.elixir }}, ${{ matrix.otp }})
+    name: Linux ${{ matrix.elixir }}, ${{ matrix.otp }}
     strategy:
       matrix:
         elixir: ["1.17.3"]
@@ -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