GHA: stop testing PHP 5.4

Author: azmeuk

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
             fail-fast: false
             matrix:
                 os: [ubuntu-latest]
-                php: ['5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4']
+                php: ['5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4']
 
         steps:
             - name: Checkout