Temporarily remove macOS from the test matrix

Author: jgarber623-cargosense

.github/workflows/ci.yml

@@ -10,15 +10,12 @@ on:
 jobs:
   test:
     name: Elixir ${{ matrix.pair.elixir }} OTP ${{ matrix.pair.otp }} (${{ matrix.os }})
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
     env:
       MIX_ENV: test
     strategy:
       fail-fast: false
       matrix:
-        os:
-          - ubuntu-latest
-          - macos-latest
         include:
           - pair:
               elixir: "1.13"