fix(tests): missing clear() #18927

This was caught in #18674 since it allows test isolation

test/functional/api/buffer_updates_spec.lua

@@ -96,6 +96,8 @@ local function reopenwithfolds(b)
 end
 
 describe('API: buffer events:', function()
+  before_each(clear)
+
   it('when lines are added', function()
     local b, tick = editoriginal(true)