Unnecessary join() when converting fstrings

[Guilouf]

Tested with the heroku online demo:

def foo():
    truc = 5
    return f'bidule {truc}'

Result:

def foo():
    truc = 5
    return ''.join(['bidule ', '{}'.format(truc)])

It works but kind of ugly, should be "bidule {}".format(truc); or with keyword argument "bidule {i}".format(i=truc)