Fixed runloop import deprecations in scroll-activity-service

[karl-sjogren]

Ember 3.27 warns about a deprecation on importing run from @ember/runloop and then using run.begin and run.end. This PR just fixes the import to avoid the warning.

deprecate.js:136 DEPRECATION: Using `run.end` has been deprecated. Instead, import the value directly from @ember/runloop:
  import { end } from '@ember/runloop'; [deprecation id: deprecated-run-loop-and-computed-dot-access]

[elwayman02]

Thanks for catching and fixing this!