fix: Updates prompt when previously selected list is unavailable

[gamebits]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Removes an unnecessary comma, and changes a plural noun to individual, in the prompt displayed when a previously selected list is no longer available.

How to test the changes in this Pull Request:

1. Insert a Newsletter Subscription Form block without having selected a list.
2. Navigate to /wp-admin/edit.php?post_type=newspack_nl_cpt&page=newspack-newsletters-settings-admin
3. Select a list
4. Reload the post editor with the form block.
5. Observe the warning message:

A previously selected list is no longer available. Please, revise the subscription list selection.

6. Merge this branch.
7. Observe the warning message:

A previously selected list is no longer available. Please revise the subscription list selection.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 24.72%. Comparing base (9212a3b) to head (4a8a1f2).

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk    #2002   +/-   ##
=========================================
  Coverage     24.72%   24.72%           
  Complexity     2932     2932           
=========================================
  Files            51       51           
  Lines         10389    10389           
=========================================
  Hits           2569     2569           
  Misses         7820     7820           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[miguelpeixe]

Thanks, Ken!

[miguelpeixe]

Whoops, we also need that change in line 309 of src/blocks/subscribe/edit.js

[leogermani]

Isn't plural the correct form here? It's the subscription lists settings..

[gamebits]

Isn't plural the correct form here? It's the subscription lists settings..

But we can choose only one list?

Maybe a complete rewrite is needed — from "Please, revise the subscription list selection" to "Please select a list".

[leogermani]

Isn't plural the correct form here? It's the subscription lists settings..

But we can choose only one list?

Maybe a complete rewrite is needed — from "Please, revise the subscription list selection" to "Please select a list".

No, you can select more than one