Fix emails with special characters being displayed incorrectly in the subject line

[donnapep]

Proposed Changes

Resolve a customer reported issue (7774726-zen) where the email subject for the Completed Course email was being displayed incorrectly when the course title contained special characters. This was also affecting the following emails, so I fixed those as well:

Teacher Emails

• Course Assigned
• Lesson Completed
• Course Completed
• Student Sent Message
• Message Reply Received

Student Emails

• Course Completed
• Quiz Graded
• Message Reply Received

Before

After

Testing Instructions

1. Enable the emails listed above.
2. Create a course and a lesson named Converting the “How Much Caller…?”.
3. Trigger the condition under which the email sends. When sending a message (or a reply to a message), be sure to include special characters in the message.
4. Verify that the emails are sent with the correct subject lines.

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
• Legacy courses (course without blocks) are tested
• 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

[github-actions]

Test the previous changes of this PR with WordPress Playground.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 51.82%. Comparing base (05d19fa) to head (4e9c1a4).
Report is 38 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk    #7546      +/-   ##
============================================
- Coverage     51.92%   51.82%   -0.10%     
- Complexity    11265    11307      +42     
============================================
  Files           630      640      +10     
  Lines         47683    47979     +296     
  Branches        421      446      +25     
============================================
+ Hits          24759    24865     +106     
- Misses        22587    22755     +168     
- Partials        337      359      +22     

Files	Coverage Δ
...ernal/emails/generators/class-course-completed.php	100.00% <100.00%> (ø)
...al/emails/generators/class-new-course-assigned.php	96.29% <100.00%> (ø)
...s/internal/emails/generators/class-quiz-graded.php	90.62% <100.00%> (ø)
...ails/generators/class-student-completes-course.php	97.05% <100.00%> (ø)
...ails/generators/class-student-completes-lesson.php	100.00% <100.00%> (ø)
.../emails/generators/class-student-message-reply.php	94.44% <100.00%> (ø)
.../emails/generators/class-teacher-message-reply.php	95.65% <100.00%> (ø)
.../emails/generators/class-student-sends-message.php	8.33% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[github-actions]

Test the previous changes of this PR with WordPress Playground.

[github-actions]

Test the previous changes of this PR with WordPress Playground.

[github-actions]

Test the previous changes of this PR with WordPress Playground.