RSVP as explicit dependency for embroider support

[hashicc]

In an ember-try scenario for embroider compatibility this popped up:

ember-concurrency/dist/-private/cancelable-promise-helpers.js/cancelable-promise-helpers.js: ember-concurrency is trying to import from rsvp but that is not one of its explicit dependencies

Related to this file

Should RSVP be included as a dependency of ember-concurrency? Any advice for resolving this for embroider support? Thanks!