Ruby 2.5 is not supported by latest-macos

Author: okuramasafumi

.github/workflows/main.yml

@@ -9,6 +9,9 @@ jobs:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
         ruby: [2.5, 2.6, 2.7, '3.0', 3.1, 3.2, 3.3, head]
+        exclude:
+          - os: macos-latest
+            ruby: 2.5
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4