rally task start fails with tuple.index(x): x not in tuple

[frigo]

possibly linked with https://github.com/micheles/decorator/issues/104

with decorator==5.0.5 that hitted Pypi a few days ago, our rally task start fails with error:

```
ERROR rally.cli.cliutils [-] Unexpected exception in CLI: ValueError: tuple.index(x): x not in tuple
ERROR rally.cli.cliutils Traceback (most recent call last):
ERROR rally.cli.cliutils File "/home/centos/rally-tasks-test/myenv/lib64/python3.6/site-packages/rally/cli/cliutils.py", line 669, in run
ERROR rally.cli.cliutils ret = fn(*fn_args, **fn_kwargs)
ERROR rally.cli.cliutils File "/home/centos/rally-tasks-test/myenv/lib64/python3.6/site-packages/decorator.py", line 232, in fun
ERROR rally.cli.cliutils return caller(func, *(extras + args), **kw)
ERROR rally.cli.cliutils File "/home/centos/rally-tasks-test/myenv/lib64/python3.6/site-packages/rally/cli/envutils.py", line 128, in default_from_global
ERROR rally.cli.cliutils id_arg_index = f.__code__.co_varnames.index(arg_name)
ERROR rally.cli.cliutils ValueError: tuple.index(x): x not in tuple
ERROR rally.cli.cliutils

```

reverting to decorator==4.4.2 fixes it

this is the content of my requirements.txt now:
```
setuptools>=40.30.0
pip>=21.0.1
cryptography<3.4
rally-openstack
decorator==4.4.2
```

(it runs rally==3.2.0 and rally-openstack==2.1.0)

[frigo (rigault-francois)]

dup from https://bugs.launchpad.net/rally/+bug/1922707