Fix wp_mail still working for temporary users

[fjorgemota]

Fix a situation that #6855 didn't cover: Blocking wp_mail when the e-mail isn't dispatched from the frontend of the site.

Proposed Changes

• Block wp_mail calls related to temporary users even on non-frontend context;

Testing Instructions

The test for this is pretty simple, on WP-CLI, run the following commands, line by line:

remove_all_filters('wp_mail'); // To make sure that no other filter will change the data informed
wp_mail( 'user1@guest.senseilms', 'Test email', 'Hello, this is a test email.', [    'From: My Site Name <noreply@example.com>']); // Should return false on this branch, true on trunk
wp_mail( 'user1@preview.senseilms', 'Test email', 'Hello, this is a test email.', [    'From: My Site Name <noreply@example.com>']); // Should return false on this branch, true on trunk
wp_mail( 'user1@example.com', 'Test email', 'Hello, this is a test email.', [    'From: My Site Name <noreply@example.com>']); // Should return true in any scenario

Here's the code running on this branch:

This is the code running on the trunk branch:

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Acceptance criteria is met
• Decisions are publicly documented
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• New UIs match the designs
• Different user privileges (admin, teacher, subscriber) are tested as appropriate
• Code is tested on the minimum supported PHP and WordPress versions
• User interface changes have been tested on the latest versions of Chrome, Firefox and Safari
• "Needs Documentation" label is added if this change requires updates to documentation
• Known issues are created as new GitHub issues

[codecov]

Codecov Report

Merging #6868 (09fd44e) into trunk (224b1b0) will increase coverage by 0.00%.
The diff coverage is 74.52%.

@@            Coverage Diff            @@
##              trunk    #6868   +/-   ##
=========================================
  Coverage     46.87%   46.87%           
  Complexity    10189    10189           
=========================================
  Files           554      554           
  Lines         36748    36748           
  Branches        381      381           
=========================================
+ Hits          17226    17227    +1     
+ Misses        19216    19215    -1     
  Partials        306      306           

Impacted Files	Coverage Δ
assets/blocks/quiz/quiz-block/quiz-edit.js	86.66% <ø> (ø)
assets/extensions/store.js	14.08% <ø> (ø)
includes/admin/class-sensei-extensions.php	0.00% <0.00%> (ø)
includes/blocks/course-theme/class-exit-course.php	47.05% <0.00%> (ø)
includes/blocks/course-theme/class-focus-mode.php	44.44% <0.00%> (ø)
includes/class-sensei-autoloader-bundle.php	0.00% <0.00%> (ø)
includes/class-sensei-autoloader.php	0.00% <0.00%> (ø)
includes/class-sensei-bootstrap.php	0.00% <0.00%> (ø)
includes/class-sensei-emails.php	0.00% <0.00%> (ø)
includes/class-sensei-grading-user-quiz.php	0.00% <ø> (ø)
... and 17 more

... and 1 file with indirect coverage changes

---

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[fjorgemota]

I'm not a huge fan of this change: basically, I'm adding the filters here for each class.

I thought about maybe creating a method in each class just to run that add_filter and call it here, but I think the result would be...quite similar, so that's why I left it this way.

This is also the main change that fixes the issue, so..yeah, there's that.

[renatho]

Looks good and works as described!