Fix formatting error in documentation 'Program Abstraction'

[penguinfirst]

Fix a minor formatting issue in the program-abstraction.adoc: correct double asterisks (**) of FieldAccess and NewExp to single asterisks (*) for consistency with the above Exp definition.

[github-actions]

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[penguinfirst]

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[penguinfirst]

recheck

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.90%. Comparing base (cf552a6) to head (5becdd7).

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #137      +/-   ##
============================================
- Coverage     71.91%   71.90%   -0.02%     
  Complexity     4354     4354              
============================================
  Files           479      479              
  Lines         15856    15856              
  Branches       2175     2175              
============================================
- Hits          11403    11401       -2     
- Misses         3571     3574       +3     
+ Partials        882      881       -1     

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