python-pluggy: bump to 1.6.0

python-pluggy: bump to 1.6.0

Required by python-pytest >= 9.0.0, which needs pluggy >= 1.5.0.

v1.5.0 added support for deprecating specific hook parameters via
warn_on_impl_args (used by pytest 9.x hookspecs). Without this,
pytest fails to import with:
  TypeError: HookspecMarker.__call__() got an unexpected keyword
  argument 'warn_on_impl_args'

v1.6.0 changes:
- Drop Python 3.8 support
- Fix regression where get_result() on a failed Result caused the
  exception traceback to grow longer on each call
- Fix StopIteration passing through hook wrappers
- Fix Python 3.14 SyntaxWarning

Signed-off-by: Alexandru Ardelean <redacted>