fix(recaptcha): use filter for deciding whether to do reCAPTCHA check

[dkoo]

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:

See description and testing instructions in Automattic/newspack-plugin#3676.

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 23.28%. Comparing base (e855d45) to head (11d0463).
Report is 1 commits behind head on release.

Additional details and impacted files

@@            Coverage Diff             @@
##             release    #1737   +/-   ##
==========================================
  Coverage      23.28%   23.28%           
  Complexity      2709     2709           
==========================================
  Files             49       49           
  Lines          10753    10753           
==========================================
  Hits            2504     2504           
  Misses          8249     8249           

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[matticbot]

🎉 This PR is included in version 3.7.3 🎉

The release is available on GitHub release

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