Add an option to remove followers; you allow the option to add, you must allow an option to remove.
If they are spammy, you can remove the account as such by reporting it to support. I have yet to encounter this spam tactics. And itch gets abused right and left, but not with this one, as far as I know. Maybe it is rare? Or you meant something else with spammy.
Following a user is somewhat strange, and some people mistake itch for a social media site. But you do actually have a public collection and post frequently. An odd follower here and there is not uncommon.
One of my "followers" is absolutely a spammy account: https://charlesallangreen.itch.io/
This one, https://itch.io/profile/shemalefuta43 , seems weird if only because, shortly after it was created, it followed my account and someone else's (not that I can see who)...
Do I simply send an email to Itch's support email?
I do know this tactic from other sites. Create account, make profile a spam message with pay-link, follow random users and hope they visit your profile and see the payload. Or even click the links.
On itch you can see how many follows an account has. For those two accounts to be "spammy", there are two things missing.
1 The payload. I did not see any links there. No advertising. No payload. Maybe one or both have changed since or were abandoned.
2 The actual spamming. Such spam accounts follow not 3 people, they follow 300 people.
I glanced on which topics and games you post and considering the general feeling those two accounts gave, it might be genuine followers. Remember that you do have a public collection. If you change that collection your followers get notification. This is part of the intention of the following mechanics. That is what it is for.
So maybe remove those accounts from your post, as it can be considered name calling and breach of privacy.
If you have more information to support the suspicion that those are spam accounts, write a mail to itch support explaining the situation. But as I wrote above, with my current information and experience, it does not look like spam to me.