Adding the same string to a list of strings in Groovy

I want to add a line to every line in a list of lines. I wanted to do something like this

def a = 'a '
def b = 'b '

[a,b].each {
    it += 'yo'
}

assertEquals a, 'a yo'
assertEquals b, 'b yo'

      

        
        
        
      

    

But obviously it won't work.