CANTINA-954: Security: Use ambiguous error message in forgot password

[rebeccahum]

Description

We should use an ambiguous error message in the Forgot Password, since the messages confirm if a user has entered a correct username or email in the "Forgot Password" form.

Changelog Description

Updated: Forgot Password

When users hit the Forgot Password in wp-login, it will no longer confirm if their email or username exists.

Pre-review checklist

Please make sure the items below have been covered before requesting a review:

• This change works and has been tested locally (or has an appropriate fallback).
• This change works and has been tested on a Go sandbox.
• This change has relevant unit tests (if applicable).
• This change uses a rollout method to ease with deployment (if applicable - especially for large scale actions that require writes).
• This change has relevant documentation additions / updates (if applicable).
• I've created a changelog description that aligns with the provided examples.

Pre-deploy checklist

• VIP staff: Ensure any alerts added/updated conform to internal standards (see internal documentation).

Steps to Test

1. Go to wp-admin > Forgot password
2. Test with an invalid email e.g. [email protected]
3. Test with a valid username e.g. vipgo
4. Both should display the same error message

[codecov]

Codecov Report

Merging #4973 (9988539) into develop (15a311a) will increase coverage by 0.03%.
The diff coverage is 88.88%.

@@              Coverage Diff              @@
##             develop    #4973      +/-   ##
=============================================
+ Coverage      28.76%   28.79%   +0.03%     
  Complexity      4742     4742              
=============================================
  Files            278      278              
  Lines          20896    20904       +8     
=============================================
+ Hits            6010     6019       +9     
+ Misses         14886    14885       -1     

Files	Coverage Δ
security/login-error.php	37.50% <88.88%> (+37.50%)	⬆️

[WPprodigy]

This needs to be a translatable string :)