Remove PHP 7.2 and 7.3 from unit testing workflow

Author: anniefu

.github/workflows/unit.yaml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: [ '7.2', '7.3', '7.4','8.0' ]
+        php-versions: [ '7.4','8.0' ]
     name: PHP ${{ matrix.php-versions }} Unit Test
     steps:
     - name: Checkout