Fixed multiline command highlighting in Cmd2Lexer

[tleonhardt]

Fixed multiline command highlighting in Cmd2Lexer.

Previously if a command name was entered after the first line it was syntax highlighted like a command even though logically it was an argument. This PR fixes that.

[github-actions]

🤖 Hi @tleonhardt, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.48%. Comparing base (41cf712) to head (0435957).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1591      +/-   ##
==========================================
+ Coverage   99.46%   99.48%   +0.02%     
==========================================
  Files          21       21              
  Lines        4679     4685       +6     
==========================================
+ Hits         4654     4661       +7     
+ Misses         25       24       -1     

Flag	Coverage Δ
unittests	99.48% <100.00%> (+0.02%)	⬆️

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[github-actions]

🤖 I'm sorry @tleonhardt, but I was unable to process your request. Please see the logs for more details.