fix(core): workaround for GC-related test issue

[romanz]

The underlying issue seems to be caused by the GC not freeing the old session since it is reachable from the C stack, so the ImageBuffer lock is not dropped.

[github-actions]

core UI changes	device test	click test	persistence test
T2T1 Model T	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
T3B1 Safe 3	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
T3T1 Safe 5	test(screens) main(screens)	test(screens) main(screens)	test(screens) main(screens)
All	main(screens)

[matejcik]

let's not do this, it's magic with no clear mechanism of effect that can break and reappear anywhere.
plus it appears that #4871 fixes the underlying problem