Fix concurrency error

Future work: Make MastodonAuthentication immutable and Sendable.

Mastodon/Scene/HomeTimeline/HomeTimelineViewModel+Donation.swift

@@ -23,13 +23,13 @@ extension HomeTimelineViewModel {
                 accountCreationDate: accountCreatedAt)
         else { return }
 
+        let seed = Mastodon.Entity.DonationCampaign.donationSeed(
+            username: userAuthentication.username,
+            domain: userAuthentication.domain)
+        
         Task { @MainActor [weak self] in
             guard let self else { return }
 
-            let seed = Mastodon.Entity.DonationCampaign.donationSeed(
-                username: userAuthentication.username,
-                domain: userAuthentication.domain)
-
             do {
                 let campaign = try await self.context.apiService
                     .getDonationCampaign(seed: seed, source: nil).value