Test on php7.4

Author: blue32a

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
 
     strategy:
       matrix:
-        php-version: ['7.2', '7.3']
+        php-version: ['7.2', '7.3', '7.4']
 
     steps:
     - name: Setup PHP ${{ matrix.php-version }}