您不需要所有这些变量来格式化HH:MM中的时间。您的函数可以定义为：

from datetime import datetime

def getHorarioActual():
    return datetime.now().strftime('%H:%M')

这里是概念证明：

Python 3.7.5 (default,Oct 17 2019,12:16:48) 
[GCC 9.2.1 20190827 (Red Hat 9.2.1-1)] on linux
Type "help","copyright","credits" or "license" for more information.
>>> from datetime import datetime
>>> def getHorarioActual():
...     return datetime.now().strftime('%H:%M')
... 
>>> getHorarioActual()
'19:05'
>>>

您显然没有正确地调用函数，正在编写

x = getHorarioActual

而不是

x = getHorarioActual()

import datetime

def getHorarioActual():
    now = datetime.datetime.now()

    horaActual = now.hour
    minutoActual = now.minute
    auxiliar = str(horaActual)+":"+str(minutoActual)
    horarioActual = auxiliar

    return horarioActual

t = getHorarioActual()
print(t)