tests: fix newline input in DispVM editor tests
tests: fix newline input in DispVM editor tests

Just '\n' isn't enough for xdotool to enter newline.

QubesOS/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin