fix: Don't throw a warning if an output folder is specified

[DaveTryon]

As called out in #500, the code returns a warning if the manifest output folder is explicitly specified by the -m parameter. Logging a warning for normal and supported operation is bad form. It was causing grief for a team that wanted to control the output location but had a zero-warning policy on their pipeline.

Side note: The default verbosity level for logging (defined at https://github.com/microsoft/sbom-tool/blob/main/src/Microsoft.Sbom.Common/Constants.cs#L16) is Warning, so this message will only be displayed if a non-default verbosity is specified. Presumably a higher verbosity would be the first diagnostic step if a problem were to occur, so this feels unlikely to cause any real-world problems.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.73%. Comparing base (09994cd) to head (9edf5f8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #542   +/-   ##
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  Coverage   59.73%   59.73%           
=======================================
  Files         248      248           
  Lines        7572     7572           
  Branches      900      900           
=======================================
  Hits         4523     4523           
  Misses       2637     2637           
  Partials      412      412           

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[pownkel]

LGTM