Fix not being able to follow more than one hashtag (#21285)

Fixes regression from #20860

spec/controllers/api/v1/tags_controller_spec.rb

@@ -33,7 +33,11 @@ RSpec.describe Api::V1::TagsController, type: :controller do
   end
 
   describe 'POST #follow' do
+    let!(:unrelated_tag) { Fabricate(:tag) }
+
     before do
+      TagFollow.create!(account: user.account, tag: unrelated_tag)
+
       post :follow, params: { id: name }
     end