NOBUG: Prepare for 5.1

[HuongNV13]

• Added MOODLE_501_STABLE
• Moved MOODLE_405_STABLE to security

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.39%. Comparing base (95ac55b) to head (1d98404).

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #108   +/-   ##
=========================================
  Coverage     85.39%   85.39%           
  Complexity       86       86           
=========================================
  Files             2        2           
  Lines           267      267           
=========================================
  Hits            228      228           
  Misses           39       39           

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[mihailges]

Thanks, Huong, the changes look good to me.