[ticket/11529] Rename RUNNING_TESTS.txt to RUNNING_TESTS.md

PHPBB3-11529
[ticket/11529] Format markdown code correctly

PHPBB3-11529
Merge remote-tracking branch 'naderman/ticket/11529' into develop-olympus

* naderman/ticket/11529:
  [ticket/11529] Format markdown code correctly
  [ticket/11529] Rename RUNNING_TESTS.txt to RUNNING_TESTS.md