ref(grouping): Clean up `event_manager_grouping` tests

[lobsterkatie]

This does a small amount of cleanup of the tests in test_event_manager_grouping.py. Specifically:

• Use constants for grouping config names.
• Split updating group metadata into a separate test.
• Simplify test showing transaction events ignore manual fingerprinting.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (ee63ee5) 81.39% compared to head (9f72c46) 81.40%. Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #65019   +/-   ##
=======================================
  Coverage   81.39%   81.40%           
=======================================
  Files        5251     5251           
  Lines      232182   232186    +4     
  Branches    45592    45593    +1     
=======================================
+ Hits       188990   189001   +11     
+ Misses      37302    37297    -5     
+ Partials     5890     5888    -2     

see 9 files with indirect coverage changes