Before Java Village and Pillage update. If a witch hits another witch would start a fight. However this feature has been removed from 1.14 snapshot and nobody mentioned that. This feature is still in Bedrock edition now.
MC-248071
Witches no longer attack each other after 1.14
Resolved
Works As Intended
3
(Unassigned)
Confirmed
Mob behaviour, Parity
mob-behavior, vanilla-parity, witch
1.18.1
Retrieved
This seems to be intentional behavior, but until stated can not be taken as that. Witches had been added to raids in snapshot 18w47a of update 1.14, and with that, came a silent change that I could not find to be mentioned anywhere. From my testing, it seems like when witches were added to raids they had been changed to no longer make other hostile mobs aggressive towards them as seen prior.
In the below screenshots of snapshot 18w43a of update 1.14 (which is the last snapshot before witches were added to raids), you can see that the witch throws poison at me, and makes the illager aggressive towards them, which then the illager kills it.
In snapshot 18w47a of 1.14 though (which again, is when witches were added to raids), after throwing the poison at me/the illager, you can see that the illager does not become aggressive towards the witch.
This is all to say that the change could hav been made to prevent witches attacking illagers in the cross fire of raid fights then the illagers attacking them in return.