tests: kernel: timer: jitter_drift: Restore initial alignment to tick

This is a follow-up to commit 4cc21e2f.

That short sleeping before starting the test was removed together with
accuracy improvements (specifically, with moving of the first readout
of the cycle counter). Nevertheless, this tick alignment it still
needed, as without it in specific conditions the test may undesirably
fail.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>