Add PHP 7.2 to build matrix

.github/workflows/build.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: ['7.3', '7.4', '8.0']
+        php-versions: ['7.2', '7.3', '7.4', '8.0']
     name: PHP ${{ matrix.php-versions }} Test on ${{ matrix.operating-system }}
 
     steps: