[TASK] Run the unit tests up to PHP 8.3 (MyIntervals#447)

Author: oliverklee

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version: [ '7.2', '7.3' ]
+        php-version: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3' ]
 
     steps:
       - name: Checkout