tests: install pylint for functional linters

The functional linter test otherwise imports the system pylint 2.12.2.
On my system w/Python 3.12, its wrapt dependency would fail with:

    ImportError: cannot import name 'formatargspec' from 'inspect'

Signed-off-by: Brian Cain <brian.cain@oss.qualcomm.com>
Message-ID: <20260908193656.2787108-1-brian.cain@oss.qualcomm.com>
Signed-off-by: Thomas Huth <th.huth@posteo.eu>

pythondeps.toml

@@ -48,3 +48,4 @@ sphinx_rtd_theme = { accepted = ">=1.2.2", installed = "2.0.0" }
 # fetched from PyPI.
 [functests]
 pygdbmi = { accepted = ">=0.11.0.0", installed = "0.11.0.0" }
+pylint = { accepted = ">=3.0.0", installed = "3.0.0" }