Make perform_enqueued_jobs compatible with all Active Job adapters

[ghiculescu]

Motivation / Background

#37270 describes a common Active Job issue where if you try to set an adapter other than :test as your adapter in a test environment, you get some confusing results.

The most popular workaround on the issue is to add this to a setup block:

(ActiveJob::Base.descendants << ActiveJob::Base).each(&:disable_test_adapter)

This solves some issues, but causes others. bensheldon/good_job#846 is an example of an issue it causes. If you call assert_emails in an integration test, it will crash here because only the test adapter defines perform_enqueued_jobs.

I think we should fix the issue of Active Job adapters being inconsistent across tests fully, and #48585 is my work in progress for that. But I wanted to extract this fix from that PR since I think it's useful in isolation.

Detail

With this PR, perform_enqueued_jobs will yield if a block is given but the test adapter is not being used. This is the minimum required to make that method compatible with any adapter.

Additional information

ref: bensheldon/good_job#846, #37270

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.