Missing python3-decorator dependency

[Micke Nordin]

Steps to reproduce:
run the following on a freshly installed Ubuntu hirsute:
 sudo apt install fabric
 fab -H host.example.com -- uname -r

Expected result:
Kernel version of host.example.com

Actual result:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/fabric/connection.py", line 5, in <module>
    from invoke.vendor.six import StringIO
ModuleNotFoundError: No module named 'invoke.vendor.six'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/bin/fab", line 11, in <module>
    load_entry_point('fabric==2.5.0', 'console_scripts', 'fab')()
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 474, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 2846, in load_entry_point
    return ep.load()
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 2450, in load
    return self.resolve()
  File "/usr/lib/python3/dist-packages/pkg_resources/__init__.py", line 2456, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/lib/python3/dist-packages/fabric/__init__.py", line 3, in <module>
    from .connection import Config, Connection
  File "/usr/lib/python3/dist-packages/fabric/connection.py", line 10, in <module>
    from decorator import decorator
ModuleNotFoundError: No module named 'decorator'

The easy fix is to install python3-decorator, this is a dependency for the corresponding debian package in Bullseye, but not in Buster:

https://packages.debian.org/bullseye/net/fabric

vs

https://packages.debian.org/buster/net/fabric