Exclude broken argcomplete 3.7.1 from CI nox install

Exclude broken argcomplete 3.7.1 from CI nox install

argcomplete 3.7.1, released 2026-08-04, declares requires-python >=3.8
but its completers module uses PEP 585 and PEP 604 syntax in class body
annotations without ``from __future__ import annotations``.  As
argcomplete is an unconditional dependency of nox, this makes ``import
nox`` fail outright on Python 3.8 and 3.9, so every job on those
interpreters errors before the noxfile is even loaded.

Pinning nox itself does not help, as all versions in range depend on
``argcomplete<4,>=1.9.4``, which resolves to 3.7.1 regardless; the
constraint has to be on argcomplete.  The exclusion is version exact so
that an upstream fix is picked up automatically, and is a no-op on
Python 3.10 and above.

Reported upstream at https://github.com/kislyuk/argcomplete/issues/559

Change-Id: I02d92ae9dcdf7cf5ed2b836a717ec04b2cc1a3bf