refactor: correct spells to that probably intended

Make correction on the terms "intput" appearing
in sciripts/pylib/twister/twisterlib.py to "input" for all.

This type of misspellings may cause another unnoticeable misspellings,
when propagated by code completions.

(assuming that the "intput" was intended
to have the opposite meaning of "output",
which also appear on the same areas)

Signed-off-by: Kentaro Sugimoto <tarotene@gmail.com>