Add PHP 5.6 on CI.

Author: kagg-design

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        php-version: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
+        php-version: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
     name: PHP ${{ matrix.php-version }} on ${{ matrix.os }}
 
     steps: