Use recent version of PHP for PHPBench

Hopefully it will be easier to install

Author: greg0ire

.github/workflows/phpbench.yml

@@ -21,7 +21,7 @@ jobs:
     strategy:
       matrix:
         php-version:
-          - "7.1"
+          - "7.4"
 
     steps:
       - name: "Checkout"