Allow bot vs bot in ScenarioV2 and test setup

[SJuliez]

A tiny change that allows leaving the human player in a scenario with no units and thus have two bots fight it out.

Best hide whitespace when reviewing. The diff looks big, but it only surrounds the unit reader with a check if there is a unit node, new line 218

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.01%. Comparing base (d349884) to head (7920791).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5835      +/-   ##
============================================
- Coverage     29.01%   29.01%   -0.01%     
  Complexity    13923    13923              
============================================
  Files          2511     2511              
  Lines        267117   267118       +1     
  Branches      47784    47785       +1     
============================================
  Hits          77504    77504              
- Misses       185661   185662       +1     
  Partials       3952     3952              

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[Sleet01]

LGTM