Do not change phpstan phar permissions when not needed

Partial fixes #22

Author: 7-zete-7

phpstan-action.bash

@@ -25,7 +25,11 @@ else
 	phar_path="${GITHUB_WORKSPACE}/$ACTION_PHPSTAN_PATH"
 fi
 
-chmod +x "$phar_path"
+if [ ! -x "$phar_path" ];
+then
+	chmod +x "$phar_path"
+fi
+
 command_string=("phpstan")
 
 if [ -n "$ACTION_COMMAND" ]