This error message is indicating that the second argument passed to the function "array_merge() " is not an array, but instead it is a string. This function is used to merge multiple arrays into one.
The error is occurring in the "validate ()" method of the 'configModel' class located at
'/var/www/html/setup/src/magento/setup/model/configmodel.php ' on line 157. To resolve the issue you need to find out where this string is coming from and convert it into an array before passing it to 'array_merge()'
HERES WHAT YOU CAN TRY
1.check the parameters passed to the 'array_merge' function.
2. look for any code that might be modifying the input data before it is passed to the 'array_merge'
3. check if the correct data types are being passed into the function.