fix: Return failing error code on invalid parameter

[DaveTryon]

As called out in #520, the sbom generation tool is a little inconsistent in how it handles return codes, returning a value of 0 if invalid parameters are passed in. This PR adds 2 lines to explicitly set the return values after displaying help or after successful completion. The successful completion is probably not necessary since we're setting to the default value, but being explicit here is low cost and makes the code (IMO) a little clearer. There was no obvious need to have a specific error code for invalid parameters, so we reuse ExitCode.GeneralError for this case. It's trivial to add a different error code if we later decide that we need to expose more information.

Testing was simple--I ran the following script to launch the app and capture the return code. This needs to be a .bat file

@echo off
Microsoft.Sbom.DotNetTool.exe
echo %ERRORLEVEL%

Before the change, ERRORLEVEL is 0. After the change, ERRORLEVEL is 1

I also tested it with correct parameters and ensured that ERRORLEVEL was correctly set to 0

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.66%. Comparing base (5424d2f) to head (8d6e97f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #544      +/-   ##
==========================================
- Coverage   59.70%   59.66%   -0.04%     
==========================================
  Files         248      248              
  Lines        7575     7575              
  Branches      901      901              
==========================================
- Hits         4523     4520       -3     
- Misses       2639     2642       +3     
  Partials      413      413              

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[pownkel]

LGTM