[3.15] gh-153741: Harden IDLE GUI tests for newer Tk and display scaling (GH-153742...

[3.15] gh-153741: Harden IDLE GUI tests for newer Tk and display scaling (GH-153742) (#154404)

gh-153741: Harden IDLE GUI tests for newer Tk and display scaling (GH-153742)

In test_sidebar.test_mousewheel, only use the X11 <Button-4>/<Button-5> events when testing on
x11 Tk before 8.7.  Otherwise, use <Mousewheel> as on other systems.

In test_configdialog, assert the 'disabled' state flag alone instead of
the exact ttk state tuple (which transient pointer states break), and
restore the tests' method masks with addCleanup().
(cherry picked from commit a2581ebc7a93ec573f64d3a5e29cbd9053de7a1f)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>