CI: Unify linux & macOS

Signed-off-by: Takuro Ashie <[email protected]>

Author: ashie

.github/workflows/macos.yml

@@ -1,4 +1,4 @@
-name: Test on Ubuntu
+name: Test
 on:
   push:
     branches: [master]
@@ -11,8 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         ruby: [ '3.2', '3.1', '3.0', '2.7' ]
-        os:
-          - ubuntu-latest
+        os: [ 'ubuntu-latest', 'macOS-latest' ]
     name: Ruby ${{ matrix.ruby }} unit testing on ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2