Interaction/Federation does not work with IPv6 only instances

### Quick summary

After setting up the ActivityPub plugin the wordpress site successfully federates with Dual-Stack instances.
It does not work with IPv6 only instances.

GTS as an IPv6only instance logs for a following request:
````
func=httpclient.(*Client).DoOnce level=INFO method=POST url=https://WORDPRESSBLOG.ORG/wp-json/activitypub/1.0/inbox contentType="application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"" attempt=1 pubKeyID=https://EXAMPLE.COM/users/ggoerisch/main-key msg="401 Unauthorized"
```
WORDPRESSBLOG.ORG and EXAMPLE.COM are placeholders.

The Wordpress installation:

WP 6.9.4
ActivityPub 8.3.0
Blog profile only

### Steps to reproduce

- install plugin
- setup profile
- follow account in Dual-Stack account - OK
- refollow account from Dual-Stack instance - OK
- follow account on IPv6-only account - NOK Plugin throws [Unable to follow account “@USER@EXAMPLE.COM”. Please verify the account exists and try again.]
- follow wordpress from IPv6only account - NOK Error from GTS above

### Site owner impact

Between 20% and 60% of the total website/platform users

### Severity

Major

### What other impact(s) does this issue have?

Individual site owner revenue

### If a workaround is available, please outline it here.

_No response_