selftests: rds: Fix pylint warnings

Tidy up all exiting pylint errors in test.py.  No functional
changes are introduced in this patch

Signed-off-by: Allison Henderson <achender@kernel.org>
Link: https://patch.msgid.link/20260308055835.1338257-2-achender@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>