Summary:
Gamerule disableRaids does not prevent Bad Omen effect from turning into Raid Omen. However, after the Raid Omen effect runs out, the raid does not happen .
Since before the new raid system 1.21 the player did not receive the Bad Omen effect if the value disableRaids = true (when killing a pillager captain), then in the new raid system it should work like that, especially since the Bad Omen effect can also turn into Trial Omen.
That is, the Bad Omen effect will not turn into Raid Omen effect if disableRaids = true.

Steps to reproduce:

1. /gamerule disableRaids true

1. /effect give @s minecraft:bad_omen infinite

1. Find/create a village.
2. Enter it.
3. Wait 30 seconds.

Observed results:
Bad Omen turned into Raid Omen and the raid did not happen.

Expected results:
Bad Omen does not turn into Raid Omen.