Update the default PHP version in dockerfile.sh to 8.1

Author: rybakit

dockerfile.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 
 if [[ -z "$PHP_IMAGE" ]] ; then
-    PHP_IMAGE='php:8.0-cli'
+    PHP_IMAGE='php:8.1-cli'
 fi
 
 if [[ -z "$TNT_LISTEN_URI" ]]; then