Test on PHP 8.4 (#38)

Author: sanmai

.github/workflows/ci.yaml

@@ -17,7 +17,18 @@ jobs:
     strategy:
       matrix:
         operating-system: ['ubuntu-latest']
-        php-version: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
+        php-version: 
+          - '5.6'
+          - '7.0'
+          - '7.1'
+          - '7.2'
+          - '7.3'
+          - '7.4'
+          - '8.0'
+          - '8.1'
+          - '8.2'
+          - '8.3'
+          - '8.4'
 
     name: CI on ${{ matrix.operating-system }} with PHP ${{ matrix.php-version }}