Drop other OSes. Expanding coverage is out of scope.

Author: oschwald

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.operating-system }}
     strategy:
       matrix:
-        operating-system: [ubuntu-latest, windows-latest, macos-latest]
+        operating-system: [ubuntu-latest]
         php-versions: ['7.2', '7.3', '7.4']
     name: "PHP ${{ matrix.php-versions }} test on ${{ matrix.operating-system }}"
     steps: