Extend 126beta WNP to 127beta [fix #14435]

[craigcook]

One-line summary

Nimbus tooling is going to ride the beta train for another cycle so we need to extend the WNP for the next version. I kept it simple and didn't duplicate or rename the files, just expanded the view condition and added more tests.

Issue / Bugzilla link

#14435

Testing

http://localhost:8000/en-US/firefox/127.0beta/whatsnew/
http://localhost:8000/en-CA/firefox/127.0beta/whatsnew/
http://localhost:8000/en-GB/firefox/127.0beta/whatsnew/
http://localhost:8000/fr/firefox/127.0beta/whatsnew/
http://localhost:8000/de/firefox/127.0beta/whatsnew/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.44%. Comparing base (bcdee9c) to head (f665d01).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14560   +/-   ##
=======================================
  Coverage   76.44%   76.44%           
=======================================
  Files         148      148           
  Lines        7987     7987           
=======================================
  Hits         6106     6106           
  Misses       1881     1881           

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[alexgibson]

r+