Misc. typos (#8694)

Found via `codespell -q 3 --skip="./app/javascript/mastodon/locales,./config/locales"`

spec/models/account_spec.rb

@@ -559,7 +559,7 @@ RSpec.describe Account, type: :model do
     end
 
     context 'when is local' do
-      it 'is invalid if the username is not unique in case-insensitive comparsion among local accounts' do
+      it 'is invalid if the username is not unique in case-insensitive comparison among local accounts' do
         account_1 = Fabricate(:account, username: 'the_doctor')
         account_2 = Fabricate.build(:account, username: 'the_Doctor')
         account_2.valid?