Internal: Remove automated testing on PHP 7.2 and 7.3: we officially only support 7.4 now (which is a temporary situation until the release of 2.0).

.github/workflows/php.yml

@@ -14,7 +14,7 @@ jobs:
             fail-fast: false
             matrix:
                 operating-system: [ubuntu-latest]
-                php-versions: ['7.2', '7.3', '7.4']
+                php-versions: ['7.4']
 
         services:
           mysql: