patch 9.1.1869: tests: test failures with Python 3.14 and test_python3

patch 9.1.1869: tests: test failures with Python 3.14 and test_python3

Problem:  tests: test failures with Python 3.14 and test_python3
Solution: Adjust the expected error message (Yee Cheng Chin)

Python 3.14 changed the error message from "argument must be 2-item
sequence" to "argument must be 2-item tuple". Fix test to account for
that. Otherwise the error message for the `vim.current.window.cursor =
True` line would not match.

closes: #18629

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>