[perl #77408] say "a" ~~ m:nth(Mu)/a/ dies with maximum recursion depth exceeded

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# New Ticket Created by  Paweł Pabian 
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On Pisa build

$ perl6 -e 'say "a" ~~ m:nth(Mu)/a/'
maximum recursion depth exceeded
  in 'EnumMap::Capture' at line 4867:CORE.setting
  in 'EnumMap::Capture' at line 4871:CORE.setting
  in 'prefix:<|>' at line 677:CORE.setting
  in 'Cool::match' at line 2398:CORE.setting
  in 'Cool::match' at line 2398:CORE.setting
  in 'Cool::match' at line 2398:CORE.setting
  in 'Cool::match' at line 2398:CORE.setting
...